304 DR. T. CANTOR ON PELAGIC SERPENTS. 
The nostrils are small, horizontally situated, as in the genera Homalopsis and Cerbe- 
rus, and furnished with a membranous valve’, which is opened to admit the air, and 
closed to prevent the entrance-of the water. 
The venomous gland is a narrow pyriform sac, divided into numerous little cells, 
which pour the venom into a common straight duct, communicating with the superior 
opening in a remarkably small venomous fang, the structure of which is described by 
T. Smith, Esq.* 
The fresh poison is a pellucid, tasteless fluid, like that of the Cophias viridis, Merrem ; 
Vipera elegans, Daudin; Naja tripudians, Merrem ; Hamadryas ophiophagus, Cantor ; 
Bungarus annularis and ceruleus, Daudin. It possesses the property of turning litmus 
paper red’. : 
The general shape of the body is much compressed, particularly towards the abdo- 
men, so that the vertical diameter is much larger than the transverse ; the short, strong 
tail is flattened, like the blade of a two-edged sword, thus at once serving as a propel- 
ling organ, and also as a rudder to direct the movements. 
The highly-compressed form, which proves the animal to be aquatic, is calculated 
for the element in which it lives, and also for the form of the prey, consisting of fishes, 
the dimensions of which will be found exactly to correspond to those of the serpents. 
Of all serpents, these are provided with the longest, most slender, and least arched ribs, 
which articulate by an oblique oval socket, with a corresponding ball on the lower sur- 
face of the corpus vertebrarum, while the abdominal extremity of the one rib lies in con- 
tact with the same part of the opposite rib. The ribs are more freely moveable in a 
lateral than in a backward direction, the progress in the water being produced by a 
quick succession of lateral curvatures of the tail and body. The functions of the ribs, 
as organs of motion, are therefore less complicated than in those serpents, which have 
to move over, and support their bodies, on a solid surface: in the latter, as observed 
by Sir Joseph Banks*, the abdominal scuta form a number of moveable broad surfaces, 
brought into action and moved as hoofs, by the corresponding pair of ribs. This kind 
of progressive motion is not required by animals who never leave the water, the progress 
in which is accelerated by the sharp keeled form of the abdomen. 
While in all other serpents the anterior set of ribs only is subservient to respiration, 
in the pelagic, whose lung extends to the anus, the entire number assists in the per- 
formance of this function. In a specimen of Hydrophis schistosa, Schlegel, measuring 
3' 10" in length, I counted 168 pair of ribs, and 224 vertebre. 
1 One of the Indian vipers, the Vipera elegans, Daudin, is provided with a similar valve, to guard against dust 
and other foreign bodies entering the spacious nostrils. 
2 Vide the excellent memoir in Philosophical Transactions, 1818, p. 471. 
3 The same fact with the venom of the Crotalus has been noticed by Dr. Harlan, Med. and Phys. Researches, 
p. 501, et seq. 
* Philosophical Transactions, 1812, p. 163. 
