Wortman — Studies of Eocene Mammalia, etc. 39 



Akt. IV. — Studies of Eocene Mammalia in the Marsh 

 Collection, Peabody Museum ; by J. L. Wortman. 



[Continued from vol. xii, p. 432.] 

 Mesonyx obtusidens Cope. 



Numerous remains of this species are preserved in the 

 present collection, one specimen of which includes many parts 

 of the skeleton. In this one the hind limbs are more or less 

 complete, and, as the Princeton specimen which formed the 

 basis of Professor Scott's excellent memoir on this subject* is 

 more or less lacking in these parts, I give herewith a state- 

 ment of their principal characters. 



The femur is somewhat damaged, but there is evidence to 

 show that it was proportionally longer and much more slender 

 than that of Dromocyon vorax. The tibia is also longer and 

 decidedly more slender than that of either Dromocyon or the 

 Princeton specimen. As compared with the former it is actu- 

 ally longer, but at least one-third less robust. Scott gives the 

 length of the Princeton specimen as 205 mm , while the present 

 specimen measures 222-| mm . 



The same degree of elongation extends to the pes, figure 61, 

 in which the length greatly exceeds that of Dromocyon. The 

 fifth metatarsal, which is the only complete one in the Prince- 

 ton specimen, is also notably longer. It may well be that the 

 present specimen indicates the existence of another species 

 characterized by the elongation and slenderness of its limbs, 

 which are acta ally greater in this respect than in the modern 

 Greyhound ; but it will perhaps be best to regard it, for 

 the present at least, as an extreme variation of Mesonyx 

 obtusidens. I introduce in this connection a drawing of the 

 hind foot of a modern dog (Bloodhound), figure 62, in order 

 to show the comparison. 



The principal characters of the foot of M. obtusidens may 

 be briefly summarized as follows : The tuber calcis is excep- 

 tionally long and slender, indicating tremendous leverage 

 power in the extension of the foot ; the astragalus is deeply 

 grooved upon its trochlear surface, and the head is not so 

 obliquely placed as in Dromocyon. The length of the tarsus 

 considerably exceeds that of the metapodials. The internal 

 cuneiform is long and narrow, with a very small facet for the 

 rudimental first metatarsal ; the second and third metatarsals 

 are of equal length and size ; the fifth is shorter than the 

 second, which is the stoutest bone of the series ; the meta- 

 tarsals are highly compressed and interlocking ; the distal ends 

 have a distinctly canine appearance, and the keels are confined 



* Jour. Acad. Nat. Sci. Phila., 1886. 



