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The morphology, taxonomy, venom, distribution, and ecology of the sea krait, Laticauda crockeri Slevin 1934, are discussed. On the basis of morphology and neurotoxins we conclude that Laticauda crockeri is a dwarf, melanotic species recently derived from L. laticaudata, but now genetically and geographically isolated from it. Relegation of L. laticaudata wolffi to the synonymy of L. crockeri is endorsed. Laticauda crockeri is restricted to a brackish lake in the interior of Rennell Island, Solomon Islands, where it is sympatric with a population of L. colubrina. Although both species occur together in many regions of the lake, Laticauda crockeri, unlike L. colubrina, was never seen on land. Consistent differences in diet were observed in a small sample of the two species. Limited evidence suggests that L. crockeri may have a strongly seasonal pattern of reproduction. The sea snakes are primarily marine or estuarine snakes whose relationships to terrestrial snakes are currently in dispute. Traditionally all were included in the Hy- drophiidae (Smith, 1926), but McDowell (1972) has diagnosed two lineages: Hydro- phiinae (viviparous sea snakes); and Lati- cauda (oviparous sea kraits). Burger and Natsuno (1974) elevated McDowell's lin- eages to family status, while Smith et al. (1977) regarded the viviparous sea snakes and the terrestrial Australasian snakes tra

Monthly samples of three tropical snakes, Acrochordus granulatus, Cerberus rhynchops and Laticauda colubrina from a limited collecting area where they are syntopic in the central Phillippines reveal pronounced diversity in reproductive seasonality. Both sexes of A. granulatus are highly seasonal and synchronized in their reproductive activity. Testis size, spermatogenic activity and plasma androgen levels declined precipitously in the non-breeding season to the same extent as observed in typical temperate species of snakes. Spermatogenesis and androgen secretion occur concomittantly and are prenuptial, coinciding with the appearance of enlarging yolked follicles in females. Gestation time (5-8 months) in this species may repesent one of the longest for a reptile, and females probably do not breed annually. C. rhynchops is also seasonal but to a lesser extent than Acrochordus. In males, testis weight, spermatogenesis and androgen secretion show a significant increase at certain times of year, but testis regression is only partial; there is some spermatogenic activity and epididymal sperm storage in all months. Gestation periods in this ovoviviparous species are probably much shorter (perhaps 3 months) than in Acrochordus, ovulation occurs over a broader season and females probably reproduce annually. In contrast, extensive evidence for male L. colubrina and limited observations on females indicate that this oviparous species is probably completely aseasonal in its reproductive biology. A review of reproductive data on other tropical marine snakes suggests that seasonality is probably the rule with the exception of L. colubrina (and some other species of Laticauda), the only oviparous species examined. Information on climatic conditions in the study area sugests that declining photoperiod and/or temperature may be responsible for testicular regression in Cerberus and Acrochordus. Data for plasma sex steroids (testosterone, estradiol and progesterone) suggest greater variability in ovarian function than previously reported for snakes.

Kayrotypic data are presented for three species of sea kraits, Laticauda. The diploid number of L. semifasciata is 38. There is obvious female heterogamety. The diploid number of L. colubrina is 34, and female heterogamety is not obvious. Haploid counts of male L. laticaudata indicate n = 20. Karyotypic data of all sea snakes and all terrestrial elapids are reviewed. The hydrophiines are conservative in number of autosomal macrochromosomal arms and relative arm lengths. Karyotypic evolution primarily involves centric fissions and rearrangement of sex chromosomes. The genus Microcephalophis should be synonomized with Hydrophis. The Australian elapid Notechis has a karyotype that is very similar to Laticauda colubrina. This is perhaps the primitive karyotype of the elapid radiation.