Marsh Collection, Peabody Museum. 437 



Length of inferior molar and premolar series from base of 



canine 55' mm 



Length of premolars 32- 



Length of molars _ 23* 



Depth of jaw at second molar __ 18* 



Length of fourth superior premolar and first and second 



molars 23* 



Width of first molar _ 7- 



Width of second molar — 9* 



The more perfect of the lower jaws was found by Professor 

 JVIarsh, at Grizzly Buttes, where Dr. Leidy's type was collected. 

 No locality is given on the labels for the other two specimens. 



Sinopa agilis Marsh. 



Limnocyon agilis Marsh, this Journal, 1872, vol. iv, p. 202 ; 

 Stypolophus brevicalcaratus Gope, Proc. Amer. Philos. Soc, 1872, p. 469. 



The materials from which this species was originally 

 described consist of the larger part of the skeleton of a young 

 individual, somewhat crushed. There are represented numer- 

 ous vertebrae, ribs, limb bones, an almost complete fore foot, 

 and considerable portions of the skull, with nearly the entire 

 dentition. Fortunately, this specimen is supplemented by a 

 second skeleton of a somewhat older individual, in which the 

 skull is very well preserved, but the teeth are considerably 

 worn. This specimen also includes numerous parts of the 

 remainder of the skeleton, so that between the two a very 

 accurate understanding of the osteological structure may be had. 

 Upon the most careful comparison, there is no doubt of the 

 specific identity of the two specimens, and I have accordingly 

 not hesitated to use all the skull material in the restoration of 

 the skull represented in the accompanying plates, VII, VIII. 



The Skull. — The general appearance of the skull is not 

 unlike that of many living Carnivores, exhibiting an unusually 

 narrow, elongate type, with a remarkably straight, superior 

 outline, and with crests and arches of moderate proportions. 

 The skull, as a whole, is much smaller in proportion to the 

 rest of the skeleton than is usually the case among the Creo- 

 donts. In length, it holds nearly the same relation to the 

 tibia and humerus as that seen in Herpestes, and, except for the 

 length of the face in Sinopa, the other proportions are not 

 very different. This feature gives the skeleton a much more 

 modern appearance than many of its contemporaries. The 

 brain case is exceptionally long and narrow, the postorbital 

 constriction, which is well marked, being placed a little pos- 

 terior to the middle of the cranium. The facial portion is not 

 unlike that of some of the Canidae, relatively long and narrow, 

 with a considerable constriction posterior to the roots of the 



