A Remarkable Ground Sloth 19 



TAXONOMY 



Order Xenarthra 



Suborder Gravigrada 



Family Megalonychidae 



Subfamily Megalonychinae 



Genus Nothrotherium Lydekker 



Species shastense Sinclair 



Generic characters, modified from Stock : 



Skull elongate and subcylindrical ; lachrymal prominent; malar vertically ex- 

 panded with inferior process slender; frontal with large sinus; pterygoid with large 

 posterior sinus opening inward. Lower jaw slender, with spout-like predental region 

 and symphyseal ossicle. Dentition 4, \. Last superior tooth semiquadrate in cross- 

 section. Anterior caniniform teeth absent. Haemapophyses in middle part of tail 

 X-shaped. Scapula relatively small. Manus with metacarpals longer and slenderer 

 than in Mega/onyx; pollex and digit V somewhat reduced, but all the digits bore 

 functional claws. Ungual phalanx of digit II, manus, broad with convex dorsal sur- 

 face. Wing-like posterior process of calcaneum longer than in Megalonyx. Astragalus 

 resembles that of Mylodon and is more specialized than in Hafalofs or in Megalonyx 

 in adjustment to the rotation of pes to a position of rest on outer side. Metatarsal IV 

 larger than in Megalonyx; metatarsal V with lateral wing-like process. Hallux some- 

 what reduced but bore a claw; digits II, III, and IV clawed and fully functional; 

 digit V vestigial in pes. 



No trace of dermal ossicles in hide. 



Three species of North American nothrotheres have been described : 



Nothrotherium shastense Sinclair 1905 

 Nothrotherium gracilicefs Stock 191 3 

 Nothrotherium texanum Hay 191 6 



In his 1925 memoir Stock abandons his species N. gracilicefs, which was based 

 upon a skull from the Rancho la Brea, and refers it, together with all of the Rancho 

 la Brea nothrotheres, to Sinclair's species shastense. The Yale specimen under dis- 

 cussion is certainly conspecific with those from the Rancho la Brea, the variations 

 from Stock's description as reviewed above being mainly those of age, as evidenced by 

 size and relative slenderness, or such as fall within the range of variations exhibited 

 by Stock's material. 



Through the courtesy of the United States National Museum I have been able to 

 make a direct comparison between our specimen and O. P. Hay's type of Nothro- 

 therium texanum (Cat. No. 8353, U.S.N.M.). 



The latter consists of an imperfect skull without the lower jaw, found at a depth 



