40 



note originally made of the characters of these teeth, before the relations of this specimen 

 to any other in the scries had been determined by comparison. 



" The last two molars, seen from the inside, have a crown of two cusps and a hind 

 talon. The cusps are remarkable for their hight, slenderness, and sharpness, resembling 

 needle-points. They do not rise straight up; the anterior one curves gently forward 

 before it ascends, retaining a slight forward obliquity; the second cusp is more nearly 

 vertical, but little longer, and slightly inclines forward. The first and second of these 

 teeth in sitd seem to consist each of one main cusp, which is long, slender, and pointed, 

 with a fore and a hind basal cusp; they resemble the two hind molars, with the reduction 

 of the anterior cusp to a talon ; but the second of these teeth has suffered fracture, and 

 the difference in both may be due to mutilation (as I subsequently satisfied myself was the 

 case). The impression of the fore part of the jaw indicates space for five or six molars or 

 premolars, besides a canine and three or, perhaps, four incisors. There is room for two 

 molars behind the teeth in place, of equal size with them." 



The best preserved teeth in the present mandible are rather less, both absolutely and 

 in proportion to the depth of the supporting part of the jaw, than in Acliyrodon nanus ; and, 

 coupling this with the course of the mylohyoid groove, I venture to indicate the species 

 represented by the present mandibular fragment as an Achyrodon pusittw. 



Genus — Peraspalax, 1 Owen. 



Species 1. — Peraspalax talpoiues, Owen. Plate II, figs. 9, 9 a, b. 



The molar teeth of this genus, agreeing in general character with those of Amblotherium, 

 are more complex, inasmuch as they show a distinct cusp-like rising or prominence (PI. II, 

 fig. 9 b, n), from the inner side of the base of the main or external cone (p). In this 

 respect they make a nearer approach to the type of the lower molar in Didelphys (ib., c) 

 than does any of the preceding Purbeck Marsupials. The antero-intemal cusp (ib., fig. 9 b, 

 e) projects obliquely forward, and from a higher level than the shorter and smaller hind 

 basal cusp (s), above which the anterior cusp of the following molar projects, giving an 

 interlocked kind of disposition of the close-set series of molars, recalling that in Achyrodon. 



The main cone (o) is shorter and basally broader relatively than in Amblotherium, much 

 more so, therefore, than in Achyrodon. The molar teeth are also larger, and of a more 

 robust character in proportion to the jaw. This character is well seen in comparison with 

 Amblotherium mustelula (fig. 2, PI. II), a species of about the same size as that represented 

 by fig. 9. 



The present species is represented by a portion of the left mandibular ramus, with 

 the inner side exposed, retaining six molars (m 2—7) and one premolar (p 4) in situ. It shows 

 the socket and impression of the first small molar (m l), and the impressions of the three 



' TT-r/'/ja, pouch ; iiondXal, mole. 



