SYNOPSIS OF THE VERTEBRATE FAUNA OP THE PUERCO SERIES. 359 



ous fossa at the fundus, and the usual ischiadic notch and groove. The pubis is 

 slender. The ischium is tlat, and the tuberosit}^ is a convexity of the posterior edge 

 which terminates in a little angular contraction, forming a "spine." 



The fossa ligamenti teris of the femur is a fissure which runs out to the margin 

 of the head. The trochanters are large; the third moderately prominent, and partly 

 opposite to the lesser tiochanter. The rotular groove is wide and elevated, and its 

 borders are equal. The external condyle is narrower than the internal. On the 

 whole the femur is a good deal like that of the Periptychvs rhahdodoa. 



PROTOGONIA Cope. 



Proc. Amer. Phil. Soc, 1S81, p. 492 ; Tertiary Verlebrata, 1885, p. 424. Phenaeodut pt. Cope ; loc. cit., 1881, p. 493 ; 

 1885, p. 488. 



This genus was originally distinguished from Phenacodus by the presence of 

 but one external tubercle on the first superior premolar, since there are two in Phen- 

 acodus. Additional specimens show that the second external tubercle of the P. puer- 

 censis is normally rudi mental, so that that species may be jii-operly referred to Proto- 

 gonia. It is further distinguished from Phenacodus by the presence of but one 

 external cusp on the second superior premolar, in which it agi'ces again with the spe- 

 cies referred to Protogonia. The latter genus thus defined embraces live species 

 which difter as follows : 



I. Fiflli cusp present on inferior true molars. 



Last four inferior molars, .025 ; internal cusp on inferior p. m. i, rudimental P. suniensis. 



Last four inferior molars, .0:50 ; internal cusp of inferior p. m. i, large P. plitifera. 



II. Fifth cusp wanting from inferior molars, except sometimes m. i. 



First superior premolar with rudimental second e.xternal cusp ; inferior true molars, .020 ; last robust premolars with 



no. or tubercular heels /'. puerceiisis. 



Inferior true molars, .020 ; last small ; premolars with wide, flat, smooth heels /*. calccohita. 



As may be seen from the catalogue of species, the material representing this 

 genus is quite abundant. This is true only of jaws and teeth, for identi liable parts 

 of skeletons are yet very rare. A very much damaged cranium of the P. puercensis 

 displays nearly all the dentition, the iuci.sors and the fourth premolar being ab.sent. 

 The first and second premolars only have internal cu.sps. In the superior canines 

 the vertical direction is the same as is seen in Ilaploconus sp. 



The fifth cusp is wanting from the last inferior true molar in the 7*. y>^/c//*era, 

 and is in a few specimens absent from the second also. Specific diilerence cannot bo 

 predicated on the presence or absence of this cusp, although in more specialized types, 

 its variations are of generic importance. The premolars of the lower series are spaced 

 in the P. plicifera, while they an- in close succession in the /\ puo'censis. 



A. P. S. — VOL. XVL 2t. 



