406 AMERICAN TESTUDINATA. Part II. 



genus, and also from Platypeltis ferox, by the very coarse and large tubercles 

 of the front and hind part of the carapace, which extend, behind, even over 

 the bony shield, and are there supported by prominent warts of the bony plates. 

 These bony warts exist in no other species with which I am acquainted : their 

 form is very irregular, sometimes oblong and sometimes orbicular; they also project 

 more or less. Another marked peculiarity of this species consists in the greater 

 bluntness of the extremities of the jaws, which are more rounded than in Asp. 

 spinifer. The jugal arch is also broader. The difference between the males and 

 the females is more strUiing in this species than in any other, the males being 

 regularly oval, whilst the females are almost circular in their outline. I have 

 noticed no difference between the coloration of this species and that of Asp. 

 spinifer, except that in younger specimens of As]3. asper there are, as in Platy- 

 peltis ferox, two or three black lines sepai'ating the jDale rim of the posterior 

 margin, whilst there is only one in Asp. spinifer; these lines are, however, closer 

 together, and fade away sooner than in Platypeltis ferox. This combination of 

 external characters, partly resembling Asp. spinifer and partly Plat, ferox, explains 

 how these species could be mistaken as one. Indeed, were it not for their 

 generic characters, a series of specimens might easily be selected, showing every 

 possible transition between them. I do not know, in the whole animal kingdom, 

 another type, in which the importance of the study of the generic characters, 

 prior to distinguishing species, is brought more forcibly before the student, than 

 the family of Trionychidse, unless it be that of CinosternoidEe. 



Thus far I have had no opportunity of examining the eggs of this species ; nor 

 do I know the appearance of the young, recently hatched, unless a young speci- 

 men, sent me by Professor Baird from the north-western part of Louisiana, be 

 the young of this species. It differs but slightly from the young Aspidonectes 

 nuchalis ; it has the same large ocelli, but the bridge connecting the carapace 

 and plastron, and a longitudinal area, before and behind the bridge, are tinged 

 with black. 



AsprooNECTES NUCHALIS, Ag. I have only seen three adult specimens of this 

 species, for which I am indebted to Prof Lindsley, of Nashville, Tennessee, and 

 a number of young ones, which I owe to the kindness of Prof Baird ; the first 

 collected in Cumberland Eiver, the others in the head waters of the Tennessee 

 River. I learn from Dr. Samuel Cunningham, of Jouesboro', that, in the higher 

 tributaries of the Tennessee River, a species of Trionj-x, which I suppose to be 

 this, is found at a considerable height in the Alleghanies ; a very unexpected fact, 

 considering the prevalence of this family in warmer regions. This species differs 

 strikingly from Asp. spinifer in the much more elongated form of the male, and 

 in the great development of the marginal spines and of the tubercles upon the car- 



