EMYDIDJE. 



297 



of more and better materials, the determination of the value of these species. In establishing 

 these species the writer has drawn on all the structures that appeared to offer assistance, the 

 general form of the shell, the proportions of its various regions, the degree of the development 

 of the buttresses, the forms of the neural bones, the form of the epiplastral lip, the form and 

 size of the various scutes, etc. The condition and the variations of the same structures in 

 various living species have been examined. As a result of this study it is to be recognized 

 that in all the characters there is more or less fluctuation. We are often left in doubt whether 

 the next specimen examined will not contradict the conclusion just formed. It will require the 

 examination of many specimens to determine the range of the variations. It will be observed 

 that there exist considerable differences among the forms of the vertebral scutes, these being 

 in some cases relatively narrow and with parallel sides, in other cases relatively broad and 



.567. 368. 369. 370. 



374- 372- 37i- 



FIGS. 367-374. Echmatemys sp. indet. Portions of skeleton. No. 1 1,525 Princeton University. 



FIGS. 367-373, X3, 374, Xi. 



367. Scapula and 367*1 coracoid. 371. Pelvis, right side. 



368. Right hurnerus, dorsal surface. 372. Right femur, tibial border. 



369. Right humerus, radial border. 373. Right femur, tibia and fibula, dorsal surface. 



370. Right humerus, ventral surface. 374. Terminal and penultimate phalanges. 



with perhaps strongly bracketed sides. It is believed that some considerable reliance may be 

 placed in these forms as indicating specific differences. Little aid in the differentiation of the 

 species has been derived from the proportions of the plastral scutes. The usually well-developt 

 axillary and inguinal scutes seem to offer valuable characters. Sometimes the axillary scutes 

 extend backward and join broadly the fifth marginals; in other cases they fall far short of 

 these marginals. In some forms the inguinal scutes articulate with the sixth marginals, while 

 in others they lack much of attaining the marginals mentioned. 



As already stated, little is certainly known about the skulls of the members of this genus. 

 In the collection of fossil reptiles belonging to Princeton University there is a portion of a skull 

 of an emyd that in all probability belongs to some species of this genus. It is represented by 

 figs. II, 12 and 13 of plate 45. It resembles much the skull of Chrysemys picta, altho larger. 

 It differs especially in having the longitudinal ridge on the triturating surface of the maxilla 



