UPPER CRETACEOUS MARSUPIALIA 125 



This is the only American Cretaceous genus in which associated upper and lower 

 teeth are known, but it is none the less based on an annoyingly inadequate type. The 

 single preserved upper molar, M\ and single preserved lower molar, M>3, are both so 

 badly worn and broken that direct comparison with the previously established Lance 

 genera is difficult. It may belong to Didclphodon, as the upper molar resembles the 

 t}pe of the latter genus rather closely in size and proportions. The only striking differ- 

 ence is the apparent greater development of style D, and this may not be of generic 

 value. In this one character it is more like Ectocotwdon, but otherwise it differs more 

 markedly from Osborn's (later) genus, as indicated in the definition. So far as one 

 can judge from the lower molar, it might be the same as almost any of the largest 

 Niobrara County Lance lower molars. Its recognition as a distinct genus is provisional 

 and is justified chiefly by the importance given it by its relative completeness. 



Thlaeodon padanicus Cope 1 892 

 1892. T. fadanicus, Cope, Am. Nat., XVI, 759. 



Type. — Amer. Mus. No. 3013. Part of left lower jaw with M,s, Ps, and roots of 

 Po, and associated fragment of left maxilla with P* and broken M'. Fig'd, Cope 1892, 

 PI. XXII ; Matthew 1916, fig. 3 and Pis. V-VI. 



Horizon and Locality. — Lance, South Dakota. 



Diagnosis. — Sole known species referred to the genus. 



There is nothing to add to Matthew's detailed description of this specimen ( 1916, 

 pp. 492-6). The morphology is well illustrated in Matthew's figure, here reproduced. 



Ectoconodon Osborn 1898 

 1898. Ectoconodon, Osborn, Bui. Amer. Mus. Nat. Hist., X, 171. 



Definition. — Upper molars relatively longer (anteroposteriorly) and narrower 

 (transversely) than in Didelfhodon, with style D more strongly developed and dis- 

 tinct, and with a very small median external cuspule somewhat internal to the outer 

 edge of the stylar shelf. 



Type. — E. fetersoni Osborn. 



Distribution. — Lance and equivalents, Wyoming and Montana. 



This genus may be valid and does show definite differences from the type of 

 Didelfhodon vorax, but upon direct comparison these differences are less noteworthy 

 than might be supposed, and the continued use of the name is provisional. 



Ectoconodon fetersoni Oshorn 1898 

 1898. E. fetersoni, Osborn, Bui. Amer. Mus. Nat. Hist., X, 171. 



Lectotype.— Amer. Mus. No. 2223. Isolated upper molar. Fig'd, Osborn 1893, 

 PI. VIII, F (lower of two) ; 1898, fig. i, F (lower) ; 1907, fig. 47- F (lower). 



Syntype.— Amer. Mus. No. 2224. Isolated upper molar. Fig'd, as above, upper 



figures. 



