1892.] NATURAL SCIENCES OP PHILADELPHIA. 309 



his name. There can, however, be no doubt that all of the above 

 names refer to the same generic group, and I have taken the name 

 tirst proposed, though our knowledge of the structure of these forms 

 is entirely due to Cope, who has described and figured them with 

 great fulness. Cope^ separates Stypolophus from Sinopa on the 

 ground that in the latter the last lower molar has a rudimentary talon, 

 but in this group this character is too variable to be of generic 

 significance, though, of course, it often is so in others. The teeth 

 are unreduced in number. The anterior upper premolars are quite 

 simple except that Ps has a small deuterocone and is implanted by 

 three fangs. ^ has the composition of the sectorial among the 

 Car'nivora, consisting of large proto- and deuterocones with a small 

 tritocone forming a trenchant blade. But for its small size, this 

 tooth would be called a sectorial ; there is also a thickening of the 

 cingulum at the antero-external angle of the crown, forming a 

 minute protostyle. The first and second upper molars are alike, 

 except in size, "^ being the larger ; they are much extended trans- 

 versely, the para- and metacones are closely approximated and a 

 well developed trenchant crest runs from the latter to the postero- 

 external angle of the crown, which is longer and more prominent 

 than in Deltatherium and not, as in that genus, continuous with the 

 metacone, but separated from it by a cleft. The shifting of the outer 

 cusps inward from the external margin of the crown, which has 

 already commenced in the Puerco genus, is very marked in Sinopa. 

 The conules are rudimentary or absent, but ^ has a minute and 

 i^ a very large parastyle. ^3 is much reduced, especially in the 

 antero-posterior direction, having lost the metacone, while the para- 

 cone has moved inward nearly to the middle of the crown. The 

 inferior premolars are simple ; p^ is very small, single-rooted and 

 isolated by a diastema both in front of and behind it ; the other pre- 

 molars are twofanged and form acute compressed cones; p^ is with- 

 out accessory cusps, p^ has a small posterior and p* both anterior 

 and posterior basal cusps. M^ is conspicuously smaller than the 

 others, but has the same construction ; the trigonid is very high, 

 especially the j^rotoconid ; the paraconid is more on the same fore 

 and aft line with the protoconid than in Deltatherium and the two 

 together form a correspondingly more efficient shearing blade; the 

 talon is much reduced, especially in m^, but retains its basin shape, 

 formed by the hypo- and ento-conids ; the hypoconulid is lost. In the 



^ Tertiary Vertebrata, p. 289. 



