272 PROF. HUXLEY ON THE CRANIAL AND [Apr. 6, 



The upper incisors have the ordinary canine characters ; and the 

 large outer incisor is close to the second. The canines are very 

 strong; and the first three prfemolars are thick. Although the fourth 

 preemolar has a length of only 11-5 millims., it is 7 millims. thick in 

 front. The inner cusp, however, is very small. In both specimens 

 a small but distinct cusp is developed from the anterior margin of 

 the anterior blade-like cusp of this tooth. This is an unusual 

 feature in the upper sectorial tooth of canine animals ; and I am the 

 more careful to draw attention to its existence, as, while Lund had 

 mentioned the fact, Burraeister expressly denies it : — " Der Fleisch- 

 zahn des Oberkiefers ist gauz Hundeartig, d. h. der innere Neben- 

 hocker sehr klcin ; und die iiussere Hockerreihe ohne den dritten 

 vordern Hocker, welcher den Yiverrinen zusteht" (/. c. p. 9). It 

 is to be presumed therefore that this minute cusp was absent in 

 Burmeister's specimen'. 



The crown of the first upper molar is triangular and comparatively 

 narrow, in consequence of the reduction of the cingulum and the dis- 

 appearance of the posterior inner cusp. The crown of the minute 

 second molar is nearly circular, with a median depression separating 

 rudimentary outer and inner cusps (fig. 1 6, A). The lower sectorial 

 presents peculiarities already noted by previous observers. Thus, the 

 inner anterior cusp has altogether disappeared, the heel is very short, 

 and the inner posterior cusp has also vanished. The second lower 

 molar is very like the upper, its crown presenting a median depression 

 bounded outside and inside by minute cusps, of which the inner is 

 the lower (fig. 16, B, p. 2(J9). 



Tlius the dentition of Icticyon is far more different from that of 

 the ordinary Canidse than that of any other known canine animal, 

 whether recent or extinct, except Otocyon, standing in some respects 

 at the opposite pole to the latter. 



In all other points, Icticyon is not only, as Lund proved, unmis- 

 takably a member of the canine group, but it is so closely allied to 

 the other North-American Thooids, that I can only regard it as a 

 modification of the Canis cancrivorus type, analogous to that which, 

 among the Old-World Jackals, has given rise to Cyon, but carried a 

 step further. 



In North America the Thooid division is represented only by such 

 macrodont forms as C. latrans and G. lupus {occidentalis). 



The foregoing Table (XV.) gives the measurements of seven 

 crania of Caiiis latrans in the British Museum and in the Museum 

 of the Royal College of Surgeons. The exact locality of No. i. is 

 unknown; No. ii. is from Hudson's Bay; No. iii. from Grand Isle, 

 Platte Rock ; No. iv. from Medicine Creek, Nebraska ; No. v. from 

 Fort Colville ; No. vi. from Fort Kearney ; and No. vii. from 

 Columbia River. They therefore cover almost the whole extent of 

 North America in longitude, and, as might be expected, exhibit a 



' Similar but better-developed anterior basal cusps occur in the upper sectorial 

 of Otocyon, and occasionally in other Canida, as C. anthtts, C. zerda, and C. hen- 

 gaicnsis. Heuce no great taxonomic importance can be assigned to this cha- 

 racter. 



