TROPIDONOTUS DEKAYI. 55 



Though the animals of the last described genus form a very natural group in 

 having all nearly the same form of head, with cheeks well developed, and the 

 body sub-triangular, which, as well as the head, the animal can flatten at will, 

 when the ribs are elevated and drawn forwards, and scales sub-hexagonal, 

 carinated, notched posteriorly, &c. &c.; yet from the form of the tail they can 

 be readily arranged in two sections — 1. Those with the tail compressed laterally 

 and triangular, like the water-snakes of our country, as Tropidonotus fasciatus, 

 &c. 2. Those with the tail more or less cylindrical, that live on land, as 

 Tropidonotus sirtalis, d:c. The only exception to the last, would perhaps be 

 the Tropidonotus leberis, where the tail is cylindrical; and yet Mr. Peale once 

 saw it in the water, which, however, does not prove that it seeks its food in that 

 element, as do those with a triangular tail. 



The scales of this group are remarkably rough, and for what purpose is not 

 easily determined; yet it is certain that most of our serpents that are covered 

 with this form of scales either live in water or near it. This circumstance seems 

 still more curious, when it is remembered that few fish have carinated scales, as 

 in Dactylopteri, (Lacepede.) 



