EMYDID&, 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 aad 
367. 368. 369. 
374- 372: 371. 
Fics. 367-374.—Echmatemys sp. indet. Portions of skeleton. No. 11,525 Princeton University. 
Fics. 367-373, X4, 374, XI. 
367. Scapula and 367a coracoid. 371. Pelvis, right side. 
368. Right humerus, dorsal surface. 372. Right feraur, 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 Aloue 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. 11, 12 and 13 of plate 45. It resembles much the skull of Chrysemys picta, altho larger. 
It fiers especially in having the longitudinal ridge on the triturating surface of the maxilla 
