418 F. B. Loomis—Hyopsodidce. 



muscle lies just under the last molar. The teeth are in a con- 

 tinuous series but without crowding. In the upper jaw, the 

 hypocone of the last molar is merely a rudiment, indicated by 

 a slightly raised portion of the cingulum. Molars one and three 

 have a small but distinct hypocone, the cingulum running to it. 

 The first and second premolars have a single cusp while the third 

 and fourth each have inner cusps. The canines are moderate 

 and the three incisors simple. Specific characters are found 

 only in the cingulum and size of the form. The lower teeth 

 are more varied, especially the last molar. The general topo- 









Fig. 1. A typical Hyopsodus lower molar, x nat. size. 



graphy of a lower tooth with the nomenclature here used is 

 given in fig. 1. On the front part of the tooth the protoconid 

 and metaconid are the principle cusps, connected anteriorally 

 by a low curved protolophid. The inner end of this is in 

 some species developed into a tiny cusp, the possible equiva- 

 lent of the paraconid. Behind, these same two cusps are 

 usually united by a metalophid, and the hypoconid is connected 

 to the metaconid by a more or less developed ridge (hypolophid). 

 The entoconid is always feebly developed, and between it and 

 the hypoconid there is a strong hypoconulid. The fourth 

 premolar has the protoconid and deuteroconid well developed, 

 and from the former a ridge runs to the front, while a second 

 ridge runs from the same cusp to the rear, developing in some 

 species one or two cusps on the margin. The third premolar 

 is similar but simpler. 



Of the milk dentition I have seen nothing which is worthy 

 of note among so many specimens. 



The skeletal material, while rather fragmentary, gives many 

 of the characters which determine the ordinal position of 

 genus. The stout humerus is widened at the distal end and 

 pierced by a supratroclear foramen (similar to Erinaoeus). 



