64 AMERICAN MESOZOIC MAMMALIA 



Laolestes grandis, new species 



Type. — Y.P.M. No. 13727. Part of right lower jaw with M1-4, broken. 



Horizon and Locality. — Morrison formation, Quarry 9, Como Bluff, Wyoming. 



Diagnosis. — Molars about 35 per cent larger than in L. eminens. Paraconid shelf 

 less distinctly basined. Sharp, somewhat nodulated crest running down posterointer- 

 nal slope of pa'' and nearly meeting a similar crest running forward from talonid cusp. 



Dentition 



This species rests on a single specimen of very indifferent preservation, but it is so 

 clearly distinct from L. eminens that its description is obligatory. It is not certain that 

 the metaconid tip was bifid, but as the other characters of the species are such as to 

 accentuate the difference from Dryolestes it is reasonable to assume that this distinctive 

 character of Laolestes was also present. On M4 the pa'' and talonid cusp are quite as 

 internal as in the corresponding tooth of L. eminens. The pa'' is more sharply pointed 

 and the paraconid shelf, or trigonid basin, is less distinctly basined than in L. eminens. 

 Down the posterointernal face of the pa"* runs a small sharp crest, somewhat discon- 

 tinuous or nodulated, which passes onto the internal face of the base of the mc* where it 

 nearly but not quite reaches a similar crest running forward from the talonid. A simi- 

 lar ridge may be seen on the talonid of Z. eminens, although not distinct so far forward 

 as M4, but such a character has not been observed on the pa'' of that species. 



Measurements 



Length Mj ca. 1.6 



Length M3 ca. 1.7 



Length M4 1.7 



Depth of ramus below M4 inside 4.4 



? "Laolestes sp. indet. 



Material. — U.S.N.M. No. 2862. Anterior portion of left lower jaw, with 1 1-4, 

 C, and P2. Fig'd {diS Asthenodon segnis) , Marsh 1887, PI. IX, fig. 6. 



Horizon and Locality. — Morrison formation, Quarry 9, Como Bluff, Wyoming. 



This interesting fragment was referred by Marsh to his Asthenodon segnis^^ but 

 the apparent basis of the reference, supposed resemblance of the canine, was inadequate, 

 as the canine is not present in the type of this synonym of Dryolestes friscus. It is un- 

 certain whether it should be referred to Dryolestes or to Laolestes, more probably to 

 the latter. The two genera were apparently closely similar in this region. 



The incisors and canine are beautifully displayed in external view and are as in 

 Laolestes eminens. There are two mental foramina, one beneath 1 4 and C, the other 

 beneath P2. 



^' It has been erroneously supposed to be a cotype. Marsh (1887, p. 336) specifically states that his 

 PI. IX, fig. 7 is the type and that this is referred. 



