112 



flings of the others, and part of the incisor. It is represented in Fig. 31, 

 Plate VI, magnified two diameters. 



The jaw in its form, proportions, and construction, and the number of ted h 

 and their relative position, agree with the conditions in Paramys, but the form 

 of the molars is sufficiently different to refer the specimen to a different genus, 

 for which the above name has been proposed. 



The molar teeth, as in Paramys, are four in number, inserted each by 

 a pair of fangs. The crowns are quadrate and invested with enamel. 

 The triturating surface, instead of being constructed like that of the squir- 

 rels, is more like that of the rats, as seen in Fig. 32, Plate VI, in which 

 the last two molars of the specimen are represented magnified eight diam- 

 eters. The crown of the third molar exhibits two transverse lobes, or 

 ridges, joined by an intermediate narrow ridge, and the inner extremities of 

 the lobes include a trilateral tubercle. The enamel being worn away from 

 the prominences of the crown leave exposed a pair of transversely ellipsoidal 

 dentinal surfaces joined by a narrow isthmus. Upon the summit of the inter- 

 nal tubercle a small islet of dentine also appears. 



The last molar exhibits three transverse ridges or lobes, of which the 

 anterior is the thickest, the middle one the thinnest, and the posterior the 

 shortest. The anterior lobe is worn so as to exhibit a transversely elliptical 

 surface of dentine bordered with enamel. The middle ridge of the crown 

 appears sigmoid and is unworn. The posterior lobe presents an exposed islet 

 of dentine on the inner half of its length. 



The anterior molar of Mysops, like the last one, is more elongate fore and 

 aft than the two succeeding molars, but it is proportionately of less size than 

 in the rats, and has not three fangs as in these animals. 



The length of the molar series is \ of an inch. The first and fourth 

 molars are about f of a line fore and aft ; the intermediate ones about |. The 

 incisor measures about | of a line fore and aft by f transversely. The depth 

 of the lower jaw below the second molar is 2§ lines. The length of the 

 hiatus in advance of the molars is \\ lines. 



Mysops fkaternus. 



Since writing the foregoing I have received another specimen, which may 

 belong to Mysops. It was found by a Shoshone Indian, and given to Dr. 

 Carter. It consists of a portion of the right ramus of the lower jaw, repre- 



