2Qg ON THE STRUCTURE AND CLASSIFICATION 
• . 1 n.nln fusD c which is stout to the apex and slightly recurved; behind, 
“nS'.Uv oxton.l t,. this,’ is the ,„stcto-ietomal cusp, I, tvhich is about one-third the 
hl.ht of c ■ op,»site the antero-intemal ensp the crown ts very broad, while .t narrows 
,o oLlmlf the breadth posteriorly; it is thus sub-triangular in honzontal seetton; the 
main cusp c, has an outer concave slope leading to a longitudinal depression, beyond 
which the crown rises into the low antero-external cusp, a : from a. the outer border 
slopes ixisteriorly into the serrate margin, d, opposite the postero-mtemal cusp. The 
position and height ol the antero-external cusp, a, varies iii to ■, it is quite 
Tlie genus Peralestea is obviously related to Peraspalax, in which we find also, in 
this case, in the lower molars, the complete opposition of cusps. After a description 
of Peraspalax, the points of similarity and difference between these forms will be dis- 
cus.sed. 
PERASPALAX. Plate VIII, fie. 9. 
'J'liis genus is also known from a single specimen, an incomplete mtindibular 
ramus, with seven teeth m situ, and the impressions of three others. The portion of 
of tlic ramus preserved, as seen on the inner surface, is stout and well rounded, and 
lielow the canine is a partial impression of the chin which bends upwards, like that 
of Triconodon, indicating that the incisors were nearly erect. These robust features 
of the jaw, taken together with the structure of the molars, seem to place Peraspalax 
in the line of the modem DasyuridcB. 
Judging from the cast, the canine was stout and recurved, like that of Tricono- 
don. At a short distance is tlie impression of a small premolar, which was probably 
pj» 2 , as the interval is broad enough for a small pm^. The second premolar had a 
low, recurved crown with a broad heel ; had the same pattern slightly enlarged ; 
pwq is hifangcd with a high, conical crown, and strong internal cingulum ; this forms 
an unU'rior ha.sal cusp, and posteriorly encircles the base of the posterior cusp. This 
elevation of the posterior cusp of the last premolar above the cingulum is observed 
in all tlie supposed carnivorous genera of the mesozoic period. Behind this pre- 
molar is a narrow gap, which was probably filled by a true molar as there is barely 
space enough for a ])remolar of the same proportions as pm^. The drawing (PL II, 
fig. 9), accompanying Prof Owen’s memoir, gives an incorrect impression of these 
molars. In the specimen a portion of the external cusp of is preserved, and 
a ca.st of the same cusp in m^; this fact, taken with the fully preserved molars 
and m-j, leaves no doubt that the molar pattern was uniform, and that the cusps seen 
in and Wj are the internal cusps, the external cusps having been broken away. 
The tyi)ical molar pattern is seen in ; there is a high, pointed, antero-verted exter- 
nal cusp a, and directly opposite it, on the inner side of the crown, a low Conical cusp 
‘ lor the details of the Vcralestes and Peraspalax molars, see the cut illustrating the typical molars of 
meaozoic mammals, under heading Classification. 
