344 THE BRLDGER FAUNA. 



of the third premohir. There are two mental foramina, one under the second 

 and one under the fourth premolars. The incisor teeth present forwards. 



The tubercles of the true molars form two pairs, the third with a large 

 fifth lobe. These paired lobes are more or less united at the base, while the 

 pairs themselves are well separated from each other. The anterior pair is 

 a little more elevated than the posterior pair. Last premolar with longer 

 basis than first molar ; its posterior heel tubercularly plicate. The crown 

 of the penultimate premolar is a slightly compressed simple cone with elon- 

 gate base, but little shorter than that of the first molar. Molars with smooth 

 enamel ; an anterior cinguluni on the second and third. A small posterior 

 median tubercle on the second molar, and a short external cingulum from 

 the base of the posterior cone forwards, on the third. Canines very large, 

 sub-erect, enamel smooth. 



Length of molar scries 1^ 



Diameter of canine tooth 0.J3 



Length of premolars 093 



Length of premoliir No. 3 035 



Length of molar No. 1 024 



Length of molar No. 2 027 



Width of molar No. 1 - 022 



Length of molar No. 3 041 



Width of molar No. 3 024 



Depth of ramus at molar No. 2 073 



The type specimen was found by Mr. Samuel Smith at the mammoth 

 Buttes near the head of South Bitter Creek. The formation is the "Washa- 

 kie basin of the Bridger. The Achoeiwdon insolens shares with the Protop- 

 salis tigrinm and Mesonyx ossifragus the distinction of being the largest of 

 the Eocene flesh-eaters. It was a formidable beast, and a worthy associate 

 of the large Palceosyops vallidens and huge Dinocerata of the same period and 



region. 



DISSACUS Cope. 



American Naturalist, 1881, p. 1019 (November 29). 



This genus is only known from upper and lower jaws. These possess 

 a dentition much like that of Mesonyx, which diflers, however, from it in one 

 essential respect. The apices or cusps of the last two molars are double, not 

 simple as is the case in Mesonyx. This constitutes an apjiroach to Sarro- 

 thrauste^, where there are three apices to the main cusp. Two species are 

 kiHiwn, both from the beds of the Piu'rco Epoch. 



