Chap. III. GENERA OF EMYDOID.E. 445 



pointed in front. Hind foot, plantigrade. The plastron is attached and hinged 

 e.ssentially as in Emys. It is probable that the difference between the manner 

 in which the plastron is moved in the Cinosternoidae and in the Emydoidae with 

 movable sternum depends on family characters, and that a single hinge could 

 not exist in the Cinosternoida), nor a doulile one in the Emvdoid. 



Though I have examined many hundred specimens of this genus, I do not yet 

 feel justified in expressing a decided opinion respecting the value of the differ- 

 ences which I have noticed among them, as they were mostly adults. The dif- 

 ferences noticed m.ty indicate different species ; but they may also mark only vari- 

 eties. There is, however, a remarkable circumstance connected with the specimens 

 that came under my observation : their variations are limited to particular regions 

 of the country. A satisfactory investigation of this genus would therefore involve 

 the whole question of local and climatic varieties. 



CisTUDO viRGiNEA, Aff} Tlic north-castem type of the genus has the most 

 extensive range. It is found in New England, and westward as far as Michi- 

 gan, and southward as far as the Carolinas. I have received three-toed speci- 

 mens from North Carolina, through Mr. W. C. Kerr, which agreed in every other 

 respect with tho.se of New England. The young are represented PI. 4, fig. 17-19 ; 

 the eggs, PI. 7, fig. 10-14. 



CisTUDO TRiUNGUis, Aff.' The western and south-western type is remarkable for 

 having, almost nniversally, only three toes to the hind feet. Specimens from Lou- 

 isiana and Mississippi are particularly small, and of a pale yellowish color, with a 

 few spots. The eggs are represented PI. 7, fig. 15 and IG. I have received a 

 very large number of specimens from Dr. Benedict and Mr. T. C. Copes, of New 

 Orleans, all of which agree in their small size and pale color. Had I not 

 noticed a few larger specimens from the Osage River and from Georgia, I should 

 not hesitate to consider them as a distinct species. 



CisTUDO ORNATA, A(/? The north-Avestern type is round, broad, and flat, with- 

 out keel, even when young, (PI. HI., fig. 12 and 13,) while the young of Cistudo 

 virginea are always strongly keeled. I have received specimens from the Upper 

 Missouri through the Smithsonian Institution, and from loAva tlirough Dr. J. Rauch. 



CiSTUDO MAJOR, Aff. The southern and south-eastern type grows to a very 

 large size, and is more oblong than the others. I have received specimens from 

 Mobile through Dr. Nott, and from Florida through Mr. Fr. W. Putnam. 



* Tliis is the Cistudo ciirolina of most aiiiliors, Onj'cliotria Mexicana. Proc. Zool. Soc. of London, 



Grew's Toiiido vlrgliua. Gray's Emys kiiidsUT- 1840. Tiic outer toe of the hind foot fades away so 



noides is the younjr. gradually that tiic genus Onycholria cannot stand. 



" Gray lias described a three-toed Cistudo from ° Of all the Cistudo which I have seen, this is 



Mexico as a distinct genus, under the name of most likely to be a distinct species. 



