2 1 2 Bulletin American Museum of Natural History. ["Vol. XVI, 



mere cingule on the postero-internal slope of the protocone. 

 The posterior heel (hypoconulid) of the lower molars is always 

 very small, but sometimes forms a sharp narrow heel upon 

 mg ; these teeth are further distinguished by the narrow 

 primitive triangle; the paraconid is distinct on mj, but de- 

 creases on mg, mg. The lower premolars are reduced. 



(Sp. 2o) Microsyops (Mesacodon) speciosus Marsh. — Type, 

 a complete lower jaw (Yale Museum), lacking the incisive 

 border and the articular portion. The measurements corre- 

 spond with those of the other Bridger small species. The 



Fig. 40. Microsyops'i annectens. Princ. Mus. Portions of rami of two indi 

 viduals. Lower figure slightly exceeding 2 diam. 



identification with Microsyops is due to the sub-molariform 

 pattern of P4. As observed by Marsh the anterior tooth is 

 large, compressed, almost in contact with the symphysis ; sym- 

 physis not coossified; lower border of jaw produced posteriorly 

 angle slightly inflected; trigonid of lower molars very distinct. 

 (Sp. 18) Microsyops (Bathrodon) typus Marsh. — Type, a 

 lower jaw (Yale Museum), containing the molar teeth (mj- 

 m3 = i2 mm.) resembling that of Microsyops and Mesacodon, 



