Chap. III. GENERA OF TRIONYCHID.E. 403 



and Southorn States, two species, belonging to two different genera, Plat}'pelti.s 

 ferox and Aspidonectes asper ; and in the South-West, in Texas, one species, Aspi- 

 donectes Enioryi. 



111. Aspidonectes, Wai/l. 



The head is broader, and less flattened, than in Amyda. The sides of the 

 front part of the head approach each other continually, and are nearly straight 

 from behind forward. The proboscis is straight, and cut vertically ; the nostrils 

 are crescent-shaped, and subdivided by a projecting ridge arising from the middle 

 of the narrow vertical partition which separates them. The outer surface of the 

 maxillaries curves out, from the suture with the prefrontals, for about half its 

 ■width, then turns down and descends almost vertically to the alveolar edge. Thus 

 the mouth is broader, and the nose less rounded, than in Amyda. The alveolar 

 edge curves down slightly from end to end ; it is sharp, but in the adult it has 

 no teeth. The vertical alveolar surface is broadest near the front end, and nar- 

 rows thence backward. The horizontal alveolar surface is broadest at the hind 

 end, and narrows thence forward ; it descends nearly constantly from the hind to 

 the front end. There is here, as in Amyda, a large opening in the skull in 

 front of the vomer. The symphysis of the lower jaw is much shorter than in 

 Amyda, and the end of the jaw broader. The alveolar surface narrows from the 

 symphysis backward ; at its front end it descends steeply from the outer edge 

 inward, but at its hind end the inner edge is raised, so that there is a .slight 

 depression in the surface there. The alveolar edge is sharp all round. Thus 

 Ave have in this genus stronger jaws, with broader alveolar surfaces, than in 

 Amyda, and cutting, but not toothed, alveolar edges. 



Aspidonectes spinifer, A(/. All modern herpetologists seem to agree in the 

 ojiinion that Trionyx spinifer, ZeS., is identical with Tr. ferox, Sc/iu: I have 

 satisfied myself, by a direct comparison of a large number of specimens of every 

 age, that this is a mistake. It is true. Dr. Holbrook has shown ^ that there is 

 an easy water communication between the different stations occupied by these 

 Turtles ; but it does not follow, that, because animals may migrate without serious 

 obstacle over any extent of land or sea, they are necessarily the same within 

 the boundaries of such areas. The ingenious suggestion of Dr. Holbrook, intended 

 to explain the presence of a southern species in the waters of the North-Western 

 and North-Eastern States, as far as Lake Champluin, has in realit}- only put an 

 end to all further comparisons between our Trionychida;. 



' North American Ilerpet. Vol. 2, p. 15. 



