233; 
OF THE MESOZOIC MAMMALIA. 
basal cusp, not observed in Diplocijnodon. 
Peramus in this family somewhat doubtful. 
These features render the position of 
PERALESTID.E, Osborn,* * 1887. 
Uxyper molars loitJi lofty internal and several low external Cusps transversely 
opposed ^ e., separated by a Imgitudvnal valley {Peralestes) . Lower molars with a 
^ngle lofty external and several internal cusps {Peraspalax and Paurodon). Oppo- 
sition of upper and lower molars not trenchant. Molar fangs, two in lime. Premolars 
with basal cusps, variable, usually strong. % Canines single fanged. 
PERALESTES, Owen,^ :871. 
‘ Dentitiou^i-, cl, pmfH, m«. The fourth premolar has an elevated external 
cingulum and a lofty crown rising above the molar level. There are two internal 
cusps upon the molars; the antero-internal is the main one and is slightly retroverted • 
the postero-internal cusp is much lower. The outer side of the crown is a ridge 
supporting an antero-external cusp and two or three tubercles behind this. 
PERASPALAX, Owen,* 1871. 
(Syn. of Peralestes, X) Dentition— cj, pmj, m 7. The premolars have 
elevated conical crowns and a strong internal cingulum, rising to the anterior cingu- 
lum cusps and to the posterior basal cusps. The molars have a single external 
antero-verted cusp. The internal cusps consist of a high medial and low anterior and 
posterior cusps at the ends of the crown. 
PAURODON, Marsh,* 1887. 
Dentitionr—ii,, cl, pmi, m;.® The canine is large, erect and single fanged. 
b 
Phcunp. 2.i. Left lower jaw of Paurodon valens, inner and outer view; three times natural size, g, mylo- 
hyoid groove, .\fter Marsh 
Behind this is a diastema followed by a small, first premolar. The second premolar 
*Proc. .\cad., Phila., June, 1887. This is probably equivalent to the Paurodonfids:, Marsh. I have 
substituted Peraleslidte, because the above family name implies a deficient number of teeth which is the 
case only in Paurodon; secondly, the family definition, as given by Professor Marsh, would exclude the 
less modified British genera. 
* “ Mesozoic Mammalia,” p. 33. 
* “ Mesozoic Mammalia,” p. 40. 
* “Am. Jour. Sc. and Arts,” April, 1887, p. 342. 
^ It is probable that additional material will modify the formula, given above, to pm j, m y,as there is a 
considerable space between m j and the anterior rim of the coronoid process. (Plate X, fig. 8). 
