1883.] 313 [Cope. 



and 0. corrugatus ; and very probably, 0. ferox. The position of the M. 

 protogonioides, M. baldwini and M. mandibularis is uncertain, though the 

 last two are probably Oxyclceni. 



The Mioclcenus cuspidatus is distinguished among its congeners, by the 

 transverse character of its superior molar teeth, that is, by the relatively 

 smaller anteroposterior diameter as compared with the transverse ; and by 

 the prominence and acuteness of their principal cusps. They thus stand 

 at the opposite extreme of the genus from the M. turgidus, where the teeth 

 are characterized by the robustness and obtuseness of the cusps, although 

 in the triangular basis of the second superior molar they agree. The ex- 

 ternal cusps are compressed cones, and in contact at the base ; the inter- 

 mediate tubercles are small and distinct. The internal cusp is large and 

 prominent. The base of the fourth premolar is T-shaped, and is as long 

 as wide. Its internal and external cusps are well developed. The cingu- 

 lum of the true molars is complete all round on the last one, and on the 

 two others except at the internal base, where it is interrupted. The second 

 molar only displays a posterior inner tubercle of the cingulum, which is 

 small, and does not give a truncate interior outline of the crown, charac- 

 teristic of M. opisthacus, M. ferox, etc. On the ms. i and ii, the cingulum is 

 expanded at the external angles of the crown, most so anteriorly. The an- 

 terior expansion rises in a low cusp in the P-m. iv. The enamel is smooth. 



This species need only be compared with M. opisthacus and M. subtri- 

 gonus, which are of about the same size. Passing by the differences 

 already mentioned in the table, the fourth premolar has a different form 

 from that of the 'M opisthacus. In the latter it is narrower and more trans- 

 verse, and with larger conical cusps, much as in M. turgidus ; in the pres- 

 ent species it has the trilobate outline seen in M. subtrigonus. As to the 

 latter species, the teeth are wide, and the cusps smaller and separated at 

 at the base, and the cingulum is crenate and lobate, in a manner quite 

 different from the smoothness and compactness of structure seen in the 

 M. cuspidatus. 



Measurements. M. 



Length cf base of last four superior molars .026 



" " " three true molars 019 



-r.. , ~ -r, • (anteroposterior .006 



Diameters of P-m. iv < * 



<. transverse .004 



Diameters of m. i. J anteroposterior 006 



c transverse 006 



Diameters of m. ii { anteroposterior .0064 



t transverse 008 



Diameters of m. iii { anteroposterior .0045 



<- transverse 006 



D. Baldwin, discoverer. 



Chkiactjs truncatus, sp. nov. 

 The genus Chriacus m. was characterized in the Proceedings of the 



PROC. AMEE. PHILOS. SOC. XXI. 114. 2N. PRINTED JANUARY , 1884. 



