288 Dr. J. E. Gray on North American Testudinata. 



present the characters by which the genus Pseudemys is separated 

 from Emys, its being retained in the genus Emijs by no means 

 shows that the genus Pseudemys is not well founded. But on 

 this subject I will make my stand on the fact, that Emys ornata, 

 which Professor Agassiz unites with Emys venusta, and E. calli- 

 rostris, which he thinks may be the same as Pseudemys con- 

 cinna, are true Emydes, and not Pseudemydes, according to the 

 characters by which I have separated those genera in the work 

 above referred to ; and that these characters^ founded on the form 

 and development of the lower jaw, on the extent of the horny 

 sheath of the lower mandible, and on the scaling of the feet, 

 are more important anatomical characters for the foundation of a 

 genus than those used to distinguish the many genera into which 

 Professor xVgassiz proposes to separate the American Emydes, — 

 if they have any characters at all ; for it is to be observed that 

 Professor Agassiz does not give any synoptic characters for the 

 families, subfamilies, genera, or species, but only indefinite gene- 

 ral observations. 



It is curious that Professor Agassiz, who has so minutely 

 subdivided the genera of the North American Emydae, and 

 described so many new species, should have so completely over- 

 looked these important characters, both in his description and 

 figures, that he has proposed to mould into one species the 

 animals belonging to such distinct genera, founded on characters 

 that must have an important influence on the habits of the 

 species. 



Further on. Professor Agassiz observes : — " Gray describes 

 two Cinosternons from North America as new species, founded 

 upon young specimens. I confess my inability to distinguish 

 them from Cin. Pennsylvanicum. Cin. punctatum seems to me 

 to be the young male, and Cin. Hippocrepis the young female 

 with a rather narrow hind lobe to the sternum, as is occa- 

 sionally the case in Cin. Pennsylvanicum. I have seen such 

 large numbers of Cinosternum Pennsylvanicum, that I feel little 

 doubt upon this point" (p. 642). This is a very distinct and 

 positive statement, apparently founded on actual observation ; 

 but let us now examine the confidence to be placed in it. 



On turning to Professor Agassiz's account of Cinosternoida 

 proper, I find he divides the North American species into — 

 "1. Thyrosternon Pennsylvanicum, Agass.; the young are repre- 

 sented, pi. 4. f. 7, 13, and pi. 5. f. 16, 17. 3. Thyrostei-non 

 Sonoriense, Ag. ; the young are represented, pi. 5. f. 11, under 

 the name of Cinosternon Sonoriense, Le C. 3. Thyrosternon inte- 

 grum, Ag. 4. Platythyra flavescens ; they are represented, pi. 5. 

 f. 12, 15," What was my astonishment, on referring to the plates, 

 to find that the figures represented the three species 1 had 



