See the page on the caste system for a description of the various kinds of brahmins in bengal.
Bengali geneological tradition (see my main genealogy page for description of sources) has it that the Buddhist Pala kings (8th to 12th century A.D: under whom the colloquial Gaudiya Prakrit emerged and became the Bengalee language) were overthrown by the Hindu Senas, a dynasty founded in the 1070 by Hemantasena, originally a tributary of the Pala dynasty, and whose ancestors came to south western Bengal from the South. It is not clear exactly how brahminized Bengal was before the rise of the Senas: according to tradition, distressed by a lack of Brahmins in Bengal (when he wanted to do a sacrifice to get a son, or when his wife needed some ceremony, or to avoid drought), a king called AdishUra (not identified historically, see the history of the sena period) brought five brahmins from kAnyakubja or Kanauj (in present day central Uttar Pradesh; tradition names the king of kanauj as candraketu, jaYAditya, or vIrasiMha) in around 942 AD (999th year according to tradition: I am assuming that this is the sambat era: if it is instead that Shaka era, then the date would be 1077 AD. Other calculations give his time to be between 964 AD and 1060 AD; there are also dates as old as 942, 932 or even 732 AD in tradition).
Speaking in detail, there seem to be three major traditions which give the old dates: the rADh.I kulajis cite 668 zAka (746 AD), whereas vAcaSpatimizra and the vArendra kulapaJjis give 654 zAka (732 AD). The brAhmaNas named by the kulAcAryas like eD.umizra, harimizra, devIvara etc. are ksitIza, medhAtithi or tithimedha, vItarAga, sudhAnidhi, and saubhari, and they came to the king AdizUra. vAcaSpati and other rADh.I kulaji writers call them bhaTTanArAYaNa, dakSa, chAndaD.a, harSa, and vedagarbha; whereas the vArendra texts call them nArAYaNa, suSeNa, dharAdhara, gautama, and parAzara. These have been rationalized as described below, but the variety of traditions (and the facts that AdizUra is described as rule of Bengal, Orissa, paJca gauD.a, aGga, kaliGga, Kerala, kAmarUpa, saurASTra, magadham mAlava, and gurjara; his dates being given as 654, 675, 804, 854, 864, 914, 954, and 999 zAka; and the ceremonies being given variously as cAndrAYaNavrata, agnihotrIYayajJa, putreSTiyajJa, or vAajapeYa) are the hallmarks of the mythical mind.
The late traditions, which match the generation times the best, are again the most unlikely to be historical: bhaTTa bhavadeva's bhuvanezvara prazasti (by vAcaSpati) talks about his sAvarNa ancestors living in siddhala with no hint of migration, even though describing events probably from the 10th century. On the other hand, the zAka era came into use in Bengal only in about the 12th century AD, so the early tradition must, at the very least, have been reworked later. Moreover, brahmins in Bengal are mentioned much earlier: e.g., sAmavedI varAhasvamin in the dhanAidaha copper plate (c. 433 AD), three vAjaseneYa brahmins in the kalAikuri grant (gupta era 120, i.e. c. 440 AD), and chAndogya sAmavedI bhaTTa brahmavIrasvAmin in the malliA plate (6th century AD); and they have been migrating to Bengal from lATa, madhyadeza, kolAJca, TakAri, muktAvasu and others during the pAla period.
The origin of kulinism and the gAJI (village) relations described later is also likely to be ahistorical. The rADh.i tradition attributes this to kSitizUra, grandson od AdizUra; whereas the vArendra tradition attributes it to vallAlasena. The maithila tradition already had the concept of the ancestral mUlagrAma, and does hav a gaGgaulI gAmI. The pharidpur copper plate from the sixth century already mentions the name bRhaccaTTa; and the Russelkonda plates of neTTabhaJja mentions a vandya debabhadra from bengal.
The mythic relationship of these brahmins: bhaTTanArAYaNa of Jambutar aged 70 years (some traditions say he lived from about 1007AD to 1097AD), shrIharSa of Ourambhr aged 90 years, dakSa of Kolang aged 70 years, vedagarbha of Madra aged 40 years, and chandara of Tadi aged 30 years, sons, respectively, of ksitIsha of shANdilya gotra and Dillicatvara/jAmbucatvara village, medhAtithi of bharadvAja gotra and auD.ambara village, vItarAga of kAshyapa gotra and kolAJca village, saurabhI of sAvarNa gotra and madagrAma village, and sudhAnidhi of vAtsya gotra and tAD.ita village (who were the first to be sent) to brahma, the creator, is given through his ten grandsons through svAYambhuva manu. (Some related mythological genealogy is available here.) The names and descendants (some descriptions describe the descendants as being many generations down) of these are: mArIci -> kashyapa -> kRSNa mishra -> tamishra -> o~kAra -> svarNaka -> jaYa -> vItarAga -> dakSa, atri, aGgirA -> vRhaspati -> bharadvAja -> apratiratha -> kaNva -> dhIra -> medhAtithi -> shrIharSa, pulasta, pulaha, bhRgu, kratu, vashiSTha, pracetA -> ruci -> shANDilya -> kalivyAsa -> vAmadeva -> ksitIsha -> bhaTTanArAYaNa, and nArada. BhRgu had two sons: cyavana and bhArgava -> shenakhaNDa -> mahAvedI -> hari. cyavana had two sons Rcika -> jamadagni and bhramati -> ruru -> shuNaka -> shauNika. hari had two sons: sAvarNi -> saubhari -> vedagarbha, and vAtsya -> sudhAnidhi -> chhAndara. At that time, tradition has it, there were 750 families of Brahmins in all of Bengal. A sketch of the political situation in north India around that time is available.
The origin myths of the kAYastha non-brahmins are closely related: The brahmins mentioned above brought with them: marakanda ghoSa of saukAlIna gotra, virATa guha of kAshyapa gotra, dasharatha basu of gautama gotra, kAlidasa mitra of vishvAmitra gotra and puruSottama datta of maudgalya gotra. (There is a genealogy page on the web which describes one claimed line of descendants of dazaratha vasu; see also here for more genealogy and mythology of these people.) The ultimate origin of the kAYasthas is claimed to be from the son of king bhadrasena who took refuge with tAlavya and promised parashurAma that his son will renounce the sword for the pen. They are divided into the uttara (northern) rADh.i, dakSiNa (southern) rADh.i and vaGgajas (eastern). Of the vaGgajas, the guhas are considered kulina, whereas the dakSiNa rADh.i kulinas are the ghose, bose, and mitra families: the dattas were left out because they did not acknowledge the supremacy of the brahmins in front AdishUra. The non-kulinas (maulikas) among the dakSiNa rADh.is are divided into the upper kar, guha, datta, dAsa, de, pAlita, siMha, sena and the lower seventy-two families. kulinism rules are complicated: the fourth (madhyAMsa), fifth (kaniSThya), and later sons (vaMshaja) are considered of lower rank. Marriage rules also forced the eldest son of a kulina to marry a kulina of the same rank, and the maulika daughters were required to marry kulinas. The vaidya genealogy and origin myths are also available on the web.
The rADh.I (western) brahmins in bengal are said to be descended from dakSa, srIharSa, bhaTTanArAYaNa, vedagarbha, and chhAndara, and the vArendrI (northern) brahmins from their brothers: suSeNa, gautama, nArAYaNa bhaTTa (who maybe identical to bhaTTanArAYaNa), parAshara, and dharAdhara respectively. According to some the rADh.I/vArendrI split took place during bhUshUra's time, others claim that there were two kings varendra and pradyumna following AdishUra, and that is when the division took place.
The rule of the Senas saw a marked revival of the caste system and other aspects of brahminical hinduism. Vijayasena (reigned 1095-1158 A.D.) was probably the first Sena emperor. His son, vallAla sena (reigned 1158-69 A.D. by one calculation and is reputed to have started the practice of anuloma (upper caste men with lower caste women) marriage in Bengal. According to tradition, his reign started in 1066 AD. He is supposed to have been the seventh generation down from AdishUra's daughter's son. He was distressed by the lack of proper attitudes amongst the Brahmin Hindus in Bengal. He and his successor lakSmaNa sena, who reigned 1178-1205 (according to one calculation) at Nadia and was defeated by Ghurid (i.e. under Sultan Muhammad of Ghur) general IkhtiyarudDin Muhammad Bakhtiyar Khilji, tried to enforce a code of ethics on the brahmins of his days, and divided the brahmins into higher (‘kulin’ i.e. ‘by heritage’) and lower (‘vamshaj’ i.e. ‘by descent’) categories. According to tradition, the five brahmins brought by Aadishura had many sons [16 (name/village: AdivarAha/vandyaghati, vikarttana/vaTavyAla, koYa/kushAri, buD.a=gaNapati/mAsacaTaka, lAla/kusumakuli, guNamaNi/ghoSalI, shubha=bAsu/kulakulI, shAnteshvara=shAnta/seYaka, vibhu=mAdhava/AkAsha, nIla/vasuYarI, madhusUdana/karAla, mahAmati=shuNTha/dIrghAGgI, baTuka=bATu/pArihAla, gu~i=guJi/kulabhi, rAma/gaD.agaD.i, and nIpa=nRpa/kesharakunI) to bhaTTanArAYaNa, 4 to shrIharSa (dhA~dhu=sAdhu/mukhaTi, nAna=lAla/saharika=saharI, jana=janArddana/diMsAi=diNdisAhI, rAma/rAYI=rAYagAmI), 16 to dakSa (sulocana/caTTa, rAma/pAladhI, vanamAlI/parkaTI=pAkarAshI, shrIhari/simalAi, nIra/ambulI, shubha/bhurigrAmI, shambhu/tailabATI, pAlu/palasA~YI, jana/koYArI, jaTAdhara/puSalI=puSilAla, shashIdhara/bhaTTashAlI, keshava/mUlagrAmI, dhIra/guD.a, kAka/haD.a, kRSNa/poD.Ari, kautuka/pItamuNDI), 12 to vedagarbha (hala/gaGga=gAGgulI, rAjyadhara/kunda, vashiSTha/siddha, vishvarUpa/nandI, kumAra/vAlI, yogI/siYArI, rAma/puMsika or nAYArI, dakSa/SATaka=sAnteshvarI, madhusUdana/pArI=pAlI, guNAkara/nArI=nAYArI or siYArI?, madana/dAYI, mAdhava=murAri/ghaNTA=ghATAla or puMsika?), and 8 to chandara(kavi/shimbalAla, nArAYaNa=hari/kAJjArI, mahAyashA/vApulI, ravi/mahistA, dhIra/patituNDa, mano=manohara/dIghala, nIlAmbara/coTkhaNDI, vishvambhara/pUrvvagAmI; the last three were born after the count of 8 was made)] who, by tradition, gave rise to the 56 gAJi (from grAmI, grAma meaning village) brahmin families.
Line of bhaTTanArAYaNa (ancestor of vandyopAdhyAYa and others of shANDilya gotra): maheshvara is 10th in line. (This is 3 generations before jaYasAgara, the originator of all vArendrI brahmins like Lahiris.) (The other kulina's, all descendants of AdivarAha vandya were jahlAna, devala, vAmana, makaranda, maheshvara, IshAna.)
Line of shrIharSa (ancestor to mukhopAdhyAYa and others of bharadvAja gotra): shrIharSa, shrIgarbha, shrInivAsa, Araba, trivikrama, kAka, dhA~dhu, jalAsaYa, vANIshwara, guha, mAdhava, kolAhala, utsAha shows 13 generations. garuD.a, another descendant of dhA~dhu mukhaTi (here dhA~dhu, instead of being the son is shown to be 6 generations down!)
Line of dakSa (ancestor to caTTopAdhyAYa and others of kAshyapa gotra): dakSa, susena, mahAdeva, haladhara, kRSNadevam varAha, shrIdhara, vahurUpa shows 8 generations. Other descendants of sulocana caTTa (another name for susena?) that became kulina are halAYudha, shuca, aravinda, and bAGgAla.
Line of Vedagarbha (our ancestor and that of gAGgulI and others of sAvarNa gotra): vedagarbha, hemagarbha, ratnagarbha, komalAnga, shobhana, vishoka, mAngalI, SaSThIvara, shishu is 9 (8 according to other geneologies) generations. (shishu is described as decendant of hala gAGgulI.) Descendant of rAjyadhara kunda is also described as being kulina.
Line of chAndara (ancestor of ghoSAla and others of vAtsya gotra): kAnu is 4th in line. The other descendant of shrIdhara kAJjilAla who became kulina was kutUhala. In addition, shira or shiromaNi descendant of surabhi ghoSAla, govarddhana AcAryya descendant of shaGkara (=dhIra?) patituNDa also became kulina.
At this time, these five ancestors were supposed to have become 1100 families of brahmins in Bengal. Note that assuming the traditional dating, the number of years per generation turns out to be 11-13 for the line of shrIharSa, 15-16 for the line of maheshvara, 17-19 for the line of dakSa and vedagarbha, and 38 for the line of chAndara. Both the minimum and maximum of these numbers is a bit extreme, the former being unbelievable. See the main genealogy page for more on the comparison between history and tradition.
In fact, the traditional stories of the rise of kulinism are very complicated. In short, among the brahmins, 6 descendants of AdivarAha vandya, 5 of sulocana caTTa, 2 of dhAndu mukhaTi, 1 of surabhi ghoSAla, 1 of dhIra putituNda, 2 of shrIdhara kAJjilAla, 1 of hala gAGgulI and 1 of rAjyadhara kundalAla were the 19 main kulina; those of mahAmati shANdilya, rAma gaD.agaD.Im guJi kulabhI, nIpa kesharakunI, dhIra guD.a, kAka haD.a, kautuka pItamuNDI, rAma rAYI, jana diNDIsAYI, murArI ghaNTeshvarI, madhusUdana poD.ArI=pARi, ravi mahintA, shaGkara pipalAi, an coTakhaNDI guNAkara were the 14 subordinate kulinas. But six of their descendants: ThoTha and dAYI, sons of kolAhala mukho, vaSiSTha mukho, son of shaGkara, kuvera, son of dharmmAMshu vandyo, cakrapANi, son of mahAdeva and kulabhUSaNa, son of vidyanAtha vandyo did not follow the marriage rules and became vaMshaja. In addition 22 people accepted gifts from shudras and became varakulina, and were later counted as vaMshaja under king danauja mAdhava (unless there is confusion with danuja mardana).
The maintainance of kulinism required following strict marriage rules: all brahmins in Bengal divided into 36 mels which are endogamous units (sometimes called thAk), and only people who were the same number of generations down from the people belonging to the original list could marry each other. This lead to these families maintaining genealogical trees: it may be the beginning of large scale genealogical record in Bengal (Normally, in marriage rituals, seven generations along the male line of the father's side, and five along the male line on the mother's side were necessary).
These claim descent from the brothers of the five brahmins who gave rise to the rADh.i brahmins.
The descendants of nArAYaNa bhaTTa (who might be identical to bhaTTanArAYaNa) are described here.
The descendants of suSeNa, brother of dakSa, are described here.
The descendants of dharAdhara, brother of chAndara, are described here.
I don't know about gautama and parAshara. See here for some information.
These also had a division into kulina and non-kulina (kApa).
Similarly, there are stories of shyAmalavarmA (or his brother harivarmA who ruled before him) bringing five brahmins (traditionally from kanauj, though probably from the north sarasvati region and south utkal region) in shaka 1001 and giving them five villages (samatasar in pharidpur to sanaka, navadvIpa in nadIYA to bharadvaja, candradvIpa in bAkergaJj to sAvarNa, koTAlipArA in pharidpur to sANDilya, and jaYArI in rAjshAhI to vasiSTha. The similarities with AdishUra bringing five brahmins is probably not a coincidence.
These vaidika brahmins are classified into pAshcAtya (western) and dAkSiNAtya (southern) categories.
A different class of brahmins, the shakadvIpI or grahavipra brahmins, who were probably interested in astrology when settled in Bihar and Bengal, may have come to Bengal from Bihra during the rule of Shashanka. They and the bhaTTa brahmins, who may have been responsible for the common priestly tasks, were not very respected in society. The movement of these ‘ordinary’ brahmins is recorded variously as being from regions like lATa and madhyadesha, and localities like kolaJca, tarkAri, muktAvastu, hastipAda, matsyavAsa, kuntIra and caNDavAra. The shAkadvIpIs (also variously called magas, Acaryas, bhojakas, sakaldwIpIya, etc. in various parts of India) are definitely of western origin, and traditionally trace their origins to a shAkadvIpa in central asia, and may be related to the historical shaka migrations. Their origin myths, both into India and into magadha (Bihar), are also structurally similar to the origin myths of the other brahmin groups described above, but of much greater antiquity. They consider their ancestors worshippers of sun and versed in the arts of AYurveda, and in the later period in Bihar they were often worshippers of shakti.