28 SYSTEMATIC PALEONTOLOGY 



as it is long, ovoid in section at the base, and with a slight twist 

 inwardly. The inner and outer surfaces are very unequal, and sepa- 

 rated by linear, rugulose ridges. The back of the crown forms, at its 

 basal half, a thick convex tubercle crossed by the posterior dividing 

 ridge and bounded near the base by a short embracing ridge. The 

 anterior dividing ridge of the crown pursues a sigmoid course from 

 the summit postero-internally to the base antero-internally. The inner 

 and outer surfaces of the crown are conspicuously wrinkled and the 

 former has, in addition, an irregular curved ridge, terminating in a 

 basal tubercle and dividing off the anterior more wrinkled third of the 

 inner face 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 com- 

 pressed near the front. 



"Length of the crown 6 lines (12 mm.); breadth 6 lines (12 mm.); 

 thickness 4f lines (9.5 mm.)" Leidy, 1869. 



Delphinodon mento Cope. 

 Plate XVII, Figs. 1, 2. 



Cetacean Wyman, 1850, Amer. Jour. Sci., vol. x, ser. ii, pp. 230-232, figs. 4-7. 

 Squalodon mento Cope, 1867, Proc. Acad. Nat. Sci. Pbila., vol. xix, pp. 132, 144, 152. 

 Delphinodon mento Leidy, 1869, Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. vii, p. 



424, pi. XXX, figs. 7-9. 

 Delphinodon mento Cope, 1890, Amer. Nat., vol. xxiv, p. 614. 



Description. — ^^The species is " characterized from four molar teeth 

 which were between two and three times as large as those belonging to 

 Squalodon wymani (Phoca of Leidy) with similar short incurved crowns, 

 but much more rugose. One molar had a smooth compressed fang, 

 which was a little curved and with a groove on each side. The fangs 

 of others were weathered, not grooved, curved and acute." Cope, 1867. 



Occurrence. — Calvert Formation. Charles county near the Patux- 

 ent river. 



Collections. — The type is in the Museum of the Academy of Natural 

 Sciences of Philadelphia. 



