THE MAMMALIA OF THE DEEP RIVER BEDS. 65 



dimensions, they increase regularly from the first to the third. The median pair are 

 too much worn to show whether they possessed bifid crowns, but this is clearly the 

 case in the second and lateral pair; the posterior groove which indicates this struc- 

 ture is more median in position than in the modern form. The canines are shaped 

 very much as in the latter, but are shorter and diverge less towards their apices. 



The first premolar resembles the corresponding upper tooth, having a very small 

 and simple crown supported on a single root. The succeeding premolars increase 

 regularly in size up to the fourth; essentially they are all alike — compressed, trench- 

 ant, acute and quite high cones ; on M, and more distinctly on M, a posterior basal 

 cusp and cingulum appear, but they are less developed than in C latrans. 



The first, or sectorial molar, is characteristically cynoid, but retains some primi- 

 tive features. Compared with the inferior sectorial of the coyote, the following dif- 

 ferences are apparent : (1) The protoconid is relatively higher, less compressed, and 

 more conical in shape, shorter in the fore and aft dimension, and its anterior border is 

 much more steeply inclined and nearly vertical ; (2) the paraconid is lower and less 

 extended antero-posteriorly ; (3) the talon is lower, and, while it is as broad as the 

 anterior portion of the crown (trigonid), and therefore entirely different from that of 

 Temnocyon, yet its basin-like character is less emphasized than that of Oanis, owing 

 to the smaller size and less elevation of the entoconid ; the metaconid corresponds in 

 size and position to that of Cams. The differences enumerated are slight and yet 

 not without importance ; for whenever the sectorial of Cynodesmus departs in struc- 

 ture from that of Cards, it is in the direction of Dajrficenus and the creodonts. m. 2 

 diners in no tangible respect from that of the coyote. M.-3 is not so much reduced 

 as in that species and has a more elongate oval crown, which is supported on two 

 fangs, while, in the recent representatives of the family, the fang is very generally 

 single. 



IT. The Skull. The skull preserves many of the primitive characters which 

 occur in the ancient genera, such as Temnocyon and Daphcenus. This is particularly 

 marked in the long, narrow cranium, with postorbital constriction placed far back of 

 the orbits, and the short face, which is due partly to the microdont dentition and the 

 anterior position of the orbits, they being farther forward than in Canis. The basi- 

 cranial axis, as measured by Huxley's method (]S"o. 19, p. 239), is strikingly long, 

 actually exceeding that of the considerably larger skull of C. latrans. This elonga- 

 tion of the cranium docs not, however, imply a correspondingly long cerebral fossa, 

 as may be seen from the position of the postorbital constriction, which marks the 

 anterior boundary of the hemispheres, and which, in this genus, is much farther 

 removed from the orbits than in the recent members of the family, in which it follows 



