1919] Merriam: Tertiary Mammalian Faunas of Mohave Desert 543 



ISCHYKOSMILUS Merriam 



Uo"X.vp6<;, strong; a-fitkr), knife. 



Machaerodus? J. C. Merriam, Univ. Calif. Publ., Bull. Dept. Geol., vol. 4, 

 p. 171, 1905. 



Ischyrosmilus Merriam, Univ. Calif. Publ., Bull. Dept. Geol., vol. 10, p. 524, 

 1918. 



Type species Machaerodus? ischyrus Merriam from beds near McKittrick on 

 the western border of the San Joaquin Valley, California. The type is known only 

 by the mandible and inferior dentition. 



Mandible massive; flange clearly marked, relatively wide anteroposterior^, 

 slightly deeper than in Smilodon, not as strongly developed as in typical 

 Machaerodus ; length of diastema much as in Machaerodus, but shorter than in 

 Smilodon. P 3 very small, and with one root. 

 P 4 with a single posterior cusp or with in- 

 cipient division of this cusp. M t without 

 metaconid and heel. The group is known 

 only from beds referred to the Pliocene. 



Fig. 154. Mustela? buwaldi, 

 n. sp. Mandible with P, to M 1; no. 

 21323, X 1%. Ricardo Pliocene, 

 Mohave Desert, California. 



Ischyrosmilus differs from the 

 Dinietis group in the absence of M 2 , 

 absence of heel and metaconid of M x , 

 great reduction of P ;j , and in the rela- 

 tively large size of the flange below 

 the diastema. From II optophone us it 

 differs in the absence of heel and 

 metaconid of M 1; and in the somewhat greater anteroposterior diam- 

 eter of the relatively shallow flange. From typical Machaerodus it 

 differs in the greater reduction of P,, and in the greater antero- 

 posterior diameter of the relatively shallow flange. From Smilodon 

 it differs in the shorter diastema, larger flange, and more simple form 

 of the posterior lobe of P 4 . This group is nearest Machaerodus, and 

 may be considered as a subgenus under that division. The fact that 

 two forms are found which resemble each other in the general char- 

 acters through which they differ from other groups, though they are 

 evidently different specifically, seems to require recognition in the 

 classification ; particularly is this desirable when the species thus dis- 

 tinguished are in a geographic province from which other Machaero- 

 dus species of similar age are not known. 



This genus approaches the Pleistocene Smilodon more closely than 

 does any American Tertiary machaerodont thus far described. The 

 characters of the lower dentition differ from those of Smilodon only 

 in the less advanced development of the second posterior cusp of P 4 . 



