CnAP. III. GENERA OF CINOSTERNOID/E. 419 



Wagler, Dumeril and Bibruii, Fitzingcr anil others, while Gray' unites Cinostermim 

 and Staurotypus as one genus. The genus Sternothoerus, on the contrary, has 

 untlergone many .successive alterations. When first distinguished by Bell,^ it con- 

 tained, besides its true repi'esentative.s, a species also that belongs to a different 

 genus, which I have called Ozotheca.'^ Wagler having unfortunately introduced 

 another name, Pehusios, for Bell's Sternothcerus, the latter was inappropriateh' 

 limited by Fitzinger to Terrapene odorata, whilst Dumeril and Bibron* referred 

 this species to Wagler's genus Staurotypus,^ which ought, however, to embrace 

 only its original type, the St. triporcatus. All the Cinosternoida) are American.^ 

 The assumption that the movability of the sternum " indicates a close affinity 

 among these Turtles has, to this day, prevented herpetologists from perceiving the 

 family characters which distinguish the true Cinosternoidoe from the Emydoidte, 

 and likewise separate them from Sternotho3rus, as .shown above in the description 

 of these families.^ Among the many fossil Testudinata thus far described there 

 is nt)t a fragment indicating that the family of Cinosternoida3 has existed in ear- 

 lier periods. This is the more surprising as its nearest relatives, the Chelydroids 

 and the Emydoids, are well known to have existed in past ages. There is, 

 however, a peculiar character prevailing in the family of Cinosternoidaj, which it 

 is difficult to express with precision, but which may yet account for their absence. 

 Most types of animals and plants, when making their first appearance upon earth, 

 are either marked by striking peculiarities, that make them stand out boldly 

 among their contemporaries on account of their great difference, or they exhibit 

 characteristics, in which the prominent features of later types are more or less 

 blended together. Nothing of the kind exists in the Cinosternoids. On the con- 

 trary, they are, as it were, abortive Testudinata, — dwarfish in size, abrupt and quick 

 in their feeble movements, seeming young when full-grown ; and yet, assuming very 

 early the characteristic features of the adult, they are everywhere in the country 

 mistaken for young Chelydroids. In all the species of which I had an oppor- 

 tunity to examine numerous specimens I noticed marked differences between the 

 males and females, con.sisting chiefly in the form of the fronl, pa:t of the shiel 1, 

 in the length of the tail, and in the scales of the legs.^ 



* Cat. Brit. Mus., 18.34, p. 3-1. the importance of a careful discrimination between 



* Zool. .Tourn., vol. 2. p. 305. family anil generic cliaracters than the changes which 

 ' Compare [i. 2.')1. the classification of these genera has undergone. 



* Erp. gen., vol. 2, p. 358. ° The difference in the form of the shield consists 

 ' Wagler, Nat. Syst. d. Ainpli., p. 137. in the greater width of its front part in the female. 



* Compare p. 302. The tail of the male is much longer and stronger than 

 ' Compare p. 346 and 418. that of the female. There is, in the male, a patch of 

 ' See p. 346. Nothing can prove more directly rough scales in the bend between the thigh and the leg. 



