124 AMERICAN MESOZOIC MAMMALIA 



Type. — Y.P.M. No. 11827. Isolated upper molar. Fig'd, Marsh 1889A, PI. IV, 



figs. 1-3. 



Horizon and Locality. — Lance, Niobrara County, Wyoming. 

 Diagnosis. — Sole known species referable to the genus as here defined. 



The primary cusps are large and stout, but not high. The conules are small and 

 near the pa and me. The cingulum is very broad and is divided into two nearly equal 

 lobes by a deep median cleft. Both styles A and B are considerably external to a line 

 through the pa and me. B is unusually large, being higher than the pa. There is no 

 true median style, although the edge of the shelf is slightly nodulated between B and 

 the locus of D. E is large and blunt and takes the form of a ridge running externally 

 from the posterior slope of the me, while D is either absent or represented by a small 

 tubercle on the anterior slope of E. 



T hlaeodon Co^e. 1892 

 1892. Thlaeodon, Cope, Am. Nat., XXVI, 759. 



Definition. — P' very heavy, wider than long, of blunt, crushing type. M^ appar- 

 ently close to that of Ectoconodon (below), but D more conical and marginal and E a 

 ridge not reaching the external margin, also whole tooth shorter and wider as well as 

 much larger. Lower jaw short and heavy, P3 longer than wide, but blunt and heavy. 

 Both Po and P3 larger than any of the lower molars. 



Type. — T. fadanicus Cope. 



Distribution. — Lance, South Dakota. 



a.m^.-'\^ 



A.M.NaZ015 



Fig. 47. Thlaeodon padanicus, upper jaw fragment, lower jaw and crown view of 

 lower teeth, type specimen. No. 3013, three halves natural size: a.m.f., anterior 

 mental foramen. (After Matthew, 19 16.) 



