324 SYNOPSIS OF THE VERTEBRATE FAUNA OF THE PUERCO SERIES. 



of this tooth is subtriangular ; that of the fii-st and second true molars is a half ellipse ; 

 while that of the last true molar is a transverse oval, as in the two species mentioned 

 above. In this last respect it diliers from the species of Mesonyx and Dissacus, 

 where that tooth has a triangular base. Enamel delicately wrinkled where unworn. 

 In the M. cmtiquus and M. conidens, the first and second true molars have a triangu- 

 lar outline, and there is no internal cingulum. 



The occiput of this species rises into an elevated transverse crest with an oval 

 outline, like that of the Dinocerata. This is divided in front by an elevated sagittal 

 crest. The brain cavity is very small. There is a preglenoid crest. 



Measurements of Superior Molars. M. 



Length ot true mnlais 0*51 



f anteroposterior 010 



Diameters of p. m. i v \ „, „ 



I transverse "'-^ 



f anteroposterior Oil 



Diameters of m. ii -,' „,„ 



I transverse (Jtu 



f anteroposterior 008 



Diameters of m. iii -^ „,^ 



I transverse uio 



Elevation of occipital crest 058 



The ramus of the mandible has a low and elongate form, and is not very robust. 

 The inferior outline rises below the coronoid process, and the angular region is nar- 

 row and compressed. The condyle is produced posteriorly, and its articulai" face is 

 recurved backwards, and downwards, contracting to an obtuse angle. Its radial line 

 is directed nearly posteriorly. The posterior border of the ramus is concave imme- 

 diately below it. The dental foramen is below the middle of the coronoid process. 

 The mental foramen is single and is below the p. ra. iii. The symphyseal sutui-e is 

 coarse. 



The canine tooth is of moderate size (crown broken oft'). The fourth premolar is 

 one-rooted. The third and second are two-rooted. They are of equal size and small ; 

 much smaller than the p. m. i. Their crowns are low, compressed-conic, with a small 

 anterior cingulum and a short carinate heel. The p. m. i is as long anteroposteriorly 

 as any of the molars. Its crown consists of a large compressed-conic cusp directed 

 somewhat obliquely backwards, and a heel supporting two closely-appressed conic 

 cusps. The internal of these is a little posterior to the external ; the latter is slightly 

 extended towards the principal cusp. There is a low anterior basal cusp. The ante- 

 i-ior part of the true molars is more elevated than the posterior. It consists of three 

 tubei'cles as already described. The heel supports three cusps ; a large external, 

 which has a crescentic section ; a minute median, and an anteroposterior interior, 

 which is of medium size, and little elevation. The third true molar dift'ers in having 



