230 Zoological Society : — 



the south of the Austrahan region, and far between the tropical 

 islands of the Pacific. A certain proximity to land appears to be 

 necessary for their life, as they are never found in those wide marine 

 spaces which are void of islands, not being able by traversing them 

 to spread into the Neotropical or ^Ethiopian regions * ; and thus they 

 may be brought as properly as marine birds into the statement of the 

 ratio between the number of species and the area of dry land. A second 

 form, quite peculiar to this region, are Snakes covered with granular 

 tubercles, Chersydrus, Acrochordus, Xenodermiis ; without being ve- 

 nomous, they approach the Hydridce by the genus Chersydrus, an 

 inhabitant of rivers and their mouths, and with an organization like 

 that of true Sea-snakes. As the family of the Lycodontidce must be 

 assigned to the Indian and African region, each exhibiting diflPerent 

 genera, so that of the Calamaridce should be divided in the same way 

 between the Neotropical and this region, whereaa Homalosoma and two 

 species of Rhinostoma may perhaps be hereafter separated from this 

 family. The above-mentioned genera of Calamaridce are highly cha- 

 racteristic ; and the very aberrant forms which abound in India are 

 here represented by a genus of this family having no palatine teeth. 

 Those intermediate forms between the well-proportioned structure of 

 the family of Colubridee and the excessively slender one of the true 

 Tree-snakes, which I unite in one family of Dryadidce, and which are 

 so common in the Neotropical region, are feebly represented by some 

 species of Cyclophis and Gonyosoma. The genus Ahcetulla is here 

 represented by Dendrophis — one sjiecies (l). picta) extending to 

 New Guinea, another (I>. punctulata) to Australia. Dryophis is 

 found in the Neotropical region as well as in the Indian one, but 

 the species of both regions differ in dentition ; the African species 

 (D. Kirtlandii) agrees with the South American ones ; finally, Pas- 

 serita is only limited between the boundaries of the East Indies. If 

 we exclude the Hydridce, the number of venomous Colubrince is 

 far surpassed by that of the Viperina ; and all the latter exhibit the 

 peculiarity of having a pit on the side of the face, which is also found 

 in the representatives of the New World, not in those of Africa. 

 Ceylon offers a remarkable exception, producing a form without such 

 a pit. 



Among those large islands which are connected with the middle 

 Palseotropical region, none offer forms so different from those of 

 the continent and the other islands as Ceylon : it might be considered 

 the Madagascar of the Indian region. We not only find there pecu- 

 liar genera and species, not again to be recognized in other parts, 

 but even many of the common species exhibit such remarkable va- 

 rieties, as to afford ample means for creating new nominal species. 



1. Calamaria and Elaps are not represented in this island. 



* During the printing of this paper, I first heard of Sea-snakes seen near the 

 western shores of America. They were observed in considerable numbers by M. 

 Salle and Mr. Salvin, at different times, from steamers crossing the Bay of 

 Panama, and were about the size of an eel. I have not the slightest reason to 

 doubt the credibility of the observers ; but so long as we have not obtained them 

 ft will always be a question whether the animals seen were Snakes or not. 



