42'! EXTINCT MAMMALIA OF NORTH AMERICA. 



for the tooth than that contained in the jaw fragment. The length of the crown is 

 about five lines ; the breadth scarcely four lines. 



Two teeth appear as premolars in relation with the former. They have longer and 

 narrower crowns than the preceding, but otherwise have the same character. The 

 single fling is long, curved and gibbous. The best preserved of the two specimens, 

 when perfect, has had its crown about half an inch long; its breadth at base is three 

 lines and three-fourths. 



Another tooth of more robust character than the preceding, represented in figure 

 18, probably holds the relative position of a canine to them, though perhaps it does 

 not belong to the same animal. The crown is stouter than in the other teeth, but 

 like them is smooth externally and rugose, except near the apex internally. Tlie 

 fang, about half as long again as the crown, is conic and oblique, but feebly curved. 

 The length of the crown is half an inch ; the breadth three lines and three-fourtlis ; 

 the thickness two lines and three-fourths. 



DELPHINODON. 

 DelpMnodon mento. 



Squalodon menio, Cope: Proc. Ac. Nat. Sc. 1867, 132, 144, 152. 



Several isolated teeth, from the niiocene formation of Charles County, Maryland, 

 ascribed by Prof Cope to the genus Squalodon, I suspect belong to a different genus. 

 The most characteristic tooth, represented in figures 7, 8, plate XXX, supposed to be 

 a premolar, is very unlike the corresponding teeth, so far as we are acquainted with 

 them, in the distinct species of Squalodon. The crown of this tooth is subtrlhedral 

 conical, as broad as it is long, ovoid in section at base, and with a slight twist in- 

 wardly. The inner and outer surfaces are very unequal, and separated by linear, 

 rugulose ridges. The back of the crown forms, at its basal half, a thick convex 

 tubercle, crossed b}- the posterior dividing ridge, and bounded near the base by a short 

 embracing ridge. Tlie anterior dividing ridge of the crown pursues a sigmoid course 

 from the summit postero-internally to the base antero-externally. The inner and 

 outer surfaces of the crown are conspicuously wrinkled and the former, in addition, 

 exhibits an irregular curved ridge, terminating in a basal tubercle and dividing off the 

 anterior more wrinkled third of the inner surface of the crown, from the posterior 

 two-thirds of the same surface. The fang is more than three times the length of the 

 crown, strongly curved backward, slightly gibbous near the crown and compressed 

 near the point. The measurements of the specimen are as follow : 



Length of the crown, 6 lines; breadtb, 6 lines; thickness, 4 J lines. 

 Length of the fang, 19 lines; greatest breadth, 5i lines. 

 Length of the tooth along its anterior curvature, 30 lines. 



A second tooth, figure 9, plate XXX, longer and with a more robust fang and a 



