318 



F. B. Loomis — Osteology and Affinities 



manner and each carries a broad trochlea for phalangeal articu- 

 lation, and on each of these there is a prominent carina, which, 

 however, is confined to the lower side and is not as promi- 

 nent as the corresponding ones on the front metacarpals. 



The proximal phalanges are a trifle shorter than those of 

 the front foot, but otherwise similar in form. The distal and 

 ungual phalanges are also very like those of the front foot. 



The following figures give the comparative measurements 

 of the three species of Stenomylus. 





Femur 



Tibia 



Metatarsus 



Phalanges 





length 



diame- 

 ter of 

 head 



diame- 

 ter of 

 trochlea 



length 



diameter 



of 

 upperend 



32-5 



38 

 39 



length 



thickness 



1 2 3 



S. hitchcocki 

 S. gracilis 

 S. crassipes 



176 

 205 

 212 



18 

 19 



20 



31 

 34 



38-5 



210 



248 

 213 



166 



198 

 185 



11 

 12-5 



36 20 17 

 44 



Classification. 



Stenomylus Peterson 



Ann. Carnegie Museum, vol. iv, 1906, p. 41. 

 vol. iv, 1908, p. 286. 



The type species is S. gracilis, found by Peterson in the 

 Lower Harrison beds of Sioux Co., J^eb. The genus may be 

 defined as^ follows : Stenomylus is a slender member of the 

 Tylopoda, adapted to an upland life, with an extreme hypsodont 

 dentition of i.-fc.^-p.f m.|-=§|- — 44 ; the upper canines partly 

 and the lower canines wholly incisiform, the first lower 

 premolar tending the same way ; vertebral formula c.Ycl.12- 

 l.Tc.14; an elongated neck; limbs didactyl and digitigrade ; 

 magnum and trapezoid free ; and navicular and ecto-meso- 

 cuneiform free. Horizon, Lower Harrison. 



At present three species are distinguished as follows : 



/Stenomylus gracilis Peterson 



Ann. Carnegie Museum, vol. iv, 1906, 

 vol. iv, 1908, 



41. 



286. 



Distinguished "by larger size, narrower upper molars, lower 

 canine less incisiform, diastema between lower premolar 1 and 

 2 shorter, lower jaw narrower, metacarpals coossified a part of 

 their length, and in details the most specialized of the three 

 species. 



Stenomylus hitchcocki sp. nov. 



See preceding description of osteology for details. The 

 species is distinguished by its small size, relatively narrow 



