PLATURUS. 355 



and comparing, first, a portion of Russell's typical specimens, or specimens captured in the same 

 seas as those from which Russell received his examples, and, secondly, the types of Shaw and 

 Gray, I find the results of my examinations so much at variance with those of others, that it 

 is necessary to treat on all the species of this family, and not to confine myself to those alone 

 which are known or supposed to be found in the Indian seas. Moreover, our present know- 

 ledge of the geographical distribution of most of the species is extremely vague, and I have 

 reason to believe that, as in other families of snakes, so in the Sea-snakes, numerous species 

 are very local, whilst others extend over an enormous area. 



Si/nojisis of the Genera. 



A. VenU'al shields well developed, flat. 



Two pail's of frontal shields PZaiwrw*, p. 355. 



B. Ventral shields well developed, with a median ridge. 



Scales imbricate Aipysurus, p. 357. 



C. Ventral shields narrow, or rudimentary or absent. 



* Nasals separated by frontal shields. 



Ventral shields distinct to the vent Disteira, p. 358. 



** Nasals contiguous. 



Head covered with scales behind Acalyptus, p. 359. 



Head short or of moderate length, entirely shielded; lower jaw without 



notch in front Hydrophis, p. 360. 



Head of moderate length, entirely shielded ; lower jaw deeply notched 



in front Enhydrina, p. 381. 



Snout very long, spatulate Pelamis, p. 382. 



PLATURUS, Latr. 



Body subcylindrical, of moderate length. Shields of the head subnormal 

 in number and arrangement ; nostrils lateral, in a single nasal shield, both 

 nasals being separated from each other by a pair of anterior frontals. Scales 

 imbricate, smooth ; ventral shields well developed ; tail with two series of 

 subcaudals. 



This genus approaches the Land-snakes in several characters. The shields of the head 

 are very regularly disposed : there are two pairs of frontals, frequently with an azygos shield 

 between the hind pair. The nostril is lateral, piercing a single narrow nasal shield ; loreal 

 absent ; one prae- and two post-oculars. Seven upper labials, the third and fourth of which 

 enter the orbit; temporals scale-like, 1 + 2 + 3. The throat is covered by two pairs of chin- 

 shields anteriorly and by scales posteriorly, the ventrals commencing at some distance behind 

 tlie head. The scales are regularly imbricate, smooth, short, slightly rounded behind ; the 



2 z2 



