SYNOPSIS OF THE VERTEBRATE FAUNA OF THE PUEKCO SERIES. 



333 



This species exhibits characters intermediate between the types witli robust pre- 

 molars, and those with pi-emolars of narrower and more angular form. The second 

 superior pi'cmolar has no internal cus|) and is trenchant, but the first has a very large 

 internal cusp, whose base is as large as that of the external one, and which has slight 

 anterior and posterioi- cingula, but no internal or external ones. It resembles the cor- 

 responding tooth of some of the PcriptychidiB. The true molars arc those of this 

 genus, resembling those of the M. auhtrigonus. I'he external cusps arc distinct and 

 not compressed. The crown is surrounded by a cingulum except on the internal side. 

 The cingulum rises into a small cusp between the external cusps, and into a small 

 but distinct posterior internal cusp. In the inferior series the first and second pre- 

 molars ai'e enlarged and have longitudinally oval bases ; both have posterior heels, 



.If II' 



ai Jit- 



J al III 



' J ar Jir 



Fig. 5. Fig. G. 



Fig. 5. JUiocUenua opisthacus molars of both series | natural size : the cusps are lettered ; ae, anterior external ; pe, 

 posterior external ; ain, anteri(jr intermediate ; j>in., posterior intermediate ; ai, anterior internal ; pi, posterior in- 

 ternal ; 5, fifth cusp. 



Fig. fi. Chriacui priseut | natural size; teelh of both jaws. 



and the first has a small anterior one ; both are like those of Anisonchus. The in- 

 ferior true molars illustrate the transitional condition of the fifth cusp in this genus. 

 A narrow crest descends inwards from the anterior external cusp, but terminates 

 below the level of the fourth, or ojjposite inner cusp, and there is no liltli cusp, or but 

 a rudiment in the m. iii of one of the specimens. 



Measurements of Fifth Specimen. M. 



Length of superior true molars 014 



( anteroposterior OOf.'i 



Diameters of superior p. m. i < 



^transverse (i07 



( anteroposterior 00(i 



Diaractera of superior p.m. ii (spec. No. 7) < 



^ transverse 001 



Length of inferior molars (except p. m. i v) 0;i;c> 



true molars 01.5.'i 



p. m. i 0O53 



Width of inferior p. m. i 00!{ 



Length of inferior m. iii OOG 



Width " " " 003 



Depth of ramus at m. i 010 



