NATURAL SCIENCES OF PHILADELPHIA. 231 



in the sciurine animals. The crown is composed of four lobes, of 

 ■which the antero-internal is the largest and most prominent, the 

 one behind it is the smallest, and the outer ones are of interme- 

 diate size, and neai'ly equal. 



If not Sciuravus, the genus may be named Paramys. The 

 specimens probably indicate three different species of the genus, 

 mainly differing in size. 



Paramys Delicatus — The largest species was perhaps a fourth 

 less in size than the Maryland marmot, though its molar series is 

 equal in length with that of the latter, measuring three-fourths of 

 an inch. The hiatus in advance of the molars has measured about 

 three lines and a half, or about half that in the Marjdand marmot. 

 The depth of the jaw at the first molar is 6i lines, at the penul- 

 timate molar 6 lines. The incisor is 2^ lines fore and aft, and 1^ 

 lines transversely. 



The specimen upon which the species is indicated consists of 

 the greater portion of the right ramus of the lower jaw. It presents 

 two mental foramina, one below the first molar, besides that in 

 the usual position. A prominent tubercle is formed at the angle 

 of convergence of the two ridges bounding the fore part of the 

 masseteric fossa. 



Paramys delicatissimus. — The smallest species is indicated by 

 a similar specimen to the former, and was about two-thirds the 

 size of the largest species. The molar series is half an inch in 

 length. The hiatus in advance of the molars measures 2| lines. 

 The depth of the jaw at the first molar is 4^ lines, at the penulti- 

 mate molar 4 lines. The incisor is 1^ lines fore and aft, and 1 line 

 transversely. 



Paramys delicatior. — An intermediate species is apparently 

 indicated by the greater portion of a left ramus of the lower jaw. 

 The molar series has measured about 1j lines in length. The 

 jaw is 5 lines deep at the penultimate molar. The incisor is 2 

 lines fore and aft, and l^ lines transversely. 



A smaller rodent than the preceding, and of a different genus, 

 is indicated by the portion of a lower jaw containing the posterior 

 two molars, and the fangs of the two in advance. 



The constitution of the jaw is similar to that in the former 

 genus. The jaw being comparatively short and deep ; the hiatus 

 in advance of the molars short and nearly straight, and the masse- 

 teric fossa advancing only as far as the position of the penulti- 

 mate molar. The molars are inserted each by two fangs ; their 

 crowns are slightly greater fore and aft, especially the first and 

 last of the series. 



The crown of the penultimate molar in its worn condition pre- 

 sents a pair of transverse elliptical dentinal tracts united by a 

 narrow median fore-and-aft isthmus. In the slight recess of the 

 inner poles of the ellipses of dentine, a small tubercle projects 

 with a circular islet of dentine on the summit. The crown of the 



1871.] 



