PURBECK FORMATIONS. 67 



mordax. In size this third molar somewhat exceeds that in the last-described specimen 

 of Triconodoii ferox, but not so much as to justify a reference to a distinct species. 



The following exemplifications of the generic characters of u[)per or maxillary teeth of 

 Triconodon seem, from their size, to have been afforded by Tr. ferox rather than by Tr. 

 mordax. 



The subject of PL III, fig. 18, nat. size, fig. 18 a, magn. 3 diam., and b working surface 

 of teeth, magn. 3 diam., is a portion of a left maxilla, with the last two premolars and 

 the first two molars. 



The molars show much wear. A cingulum extends along the outer side of the base 

 of each ; it is impressed by many small vertical grooves or notches, and is thickest as it 

 curves toward the summit of the anterior and the posterior lobes at the two ends of the 

 tooth. The three lobes incline inward toward their summits ; but these have been much 

 worn down. The posterior fang of the second molar {m 2) is exposed at the hinder 

 fracture. The main cone of the last premolar (jo 4) has its apex worn away, not broken 

 ofi"; but this extends beyond the level of the w^orking surface of m 1 and m 2. There is a 

 hind basal cusp, as vpell as a basal ridge, or ' cingulum ' which ends behind in a slight 

 projection beyond the 'talon ' of ;o 4. The penultimate premolar (jo 3) has a slightly 

 retroverted main cone with a front and hind basal talon, the latter being most prominent. 

 The alveolus and two roots of the second premolar {p 2) are included in this fragment of 

 upper jaw, showing a decrease of size corresponding to that of the homotypal teeth of 

 the mandible. 



A portion of the bony palate is preserved {a, fig. 1 8), extending inward from the alveoh 

 oi p I, p 2 : this thin, inferiorly concave, bony plate is entire to its fractured margin. 

 There is a depression or smooth groove (0) in the maxillary bone, a short way above the 

 sockets of JO 2 ; it may indicate the position of an antorbital canal outlet. 



In PI. Ill, fig. 17 represents of the nat. size, and fig. 17 a magn. 3 diam., a portion of 

 a right maxilla, with the last two premolars, the first molar and the fore part of the second 

 molar, m situ, the inner side being exposed with a contiguous portion of the bony palate. 

 The teeth agree in size with those in the maxillary specimen of the opposite side last 

 described. 



The penultimate premolar [p 3), in like manner, shows a chief cone, with an anterior 

 and a posterior basal cup, each of the latter being girt by a ridge which almost subsides at 

 the prominent mid-part of the main cone ; the hind basal cusp is the largest. The last 

 premolar {p 4), with increase of size shows plainly the continuation of the cingulum, 

 with a tubercular character, from below the fore and hind talons, across the base of the 

 main cone, with a narrow median interruption, where the main cone seems to be longitu- 

 dinally impressed. The posterior basal cusp is relatively larger than inj» 3- The apex 

 of the main cone extends beyond the summit of the contiguous molar cones. In the 



