MARYLAND GEOLOGICAL SURVEY 9 



/?. Lumbar diapophj'ses spiniform. 



Lumbar and caudal vertebrae slender Zarachis. 



Lumbar and caudal vertebrae short Ixacanthus. 



(i/i. Lumbar diapo^jhyses wide, flat. 



Muzzle elongate, slender; cervical vertebrae ]ong. . . Prisc<Kielphinus. 



Muzzle slender, cervical vertebrae, shorter Pontoporia. 



IJL Teeth with longitudinally flattened roots. 



Teeth in entire length of maxillary bone; symphysis con- 

 nate Stenodelphis. 



Teeth in all the jaws; symphysis not connate; an erect osseus 



crest on posterior part of the maxillary Platanista. 



Teeth at the base of the maxillary only; muzzle produced into 



a subcylindrical beak RhaMostens. 



iV. No teeth; an alveolar groove; muzzle depressed, elongate .... Agahehis. 



The genus Lophocetus is not ineliiided in this scheme and it seems 

 impossible to insert it as only the skull is known. Certainly it belongs 

 in the second section; "forms with CA^lindrically rooted teeth." 



Genus PRISCODELPHINUS Cope. 



Prisgodelphinus gabbi Cope. 

 Plate X, Fig. 6. 



Belphinapterus gabbi Cope, 1868, Proc. Acad. Nat. Sci. Pbila., vol. xx, p. 191. 

 Tretosphys gabbi Cope, 1868, Proc. Acad. Nat. Sci. Phila., vol. xx, p. 191. 

 Tretosphys gabbi Cope, 1869, Proc. Acad. Nat. Sci. Phila., vol. xxi, pp. 7, 8. 

 Tretosphys gabbi Leidy, 1869, Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. vii, p. 434. 

 Priscodelphinus gabbi Cope, 1890, Amer. Nat., vol. xxiv, p. 615. 



Description. — Described from a single caudal vertebra. " It has 

 pertained to a species of not more than half the length of T. grandaevus, 

 and is less strongly constricted everywhere and especially below. In a 

 caudal of near the same position, the ridges and chevron articular 

 surfaces are much more elevated, especially those on the anterior part 

 of the centrum. They embrace a very deep groove in this, a shallow 

 one in the T. gahhi. An additional longitudinal ridge on each side the 

 inferiors in front is wanting in T. gabhi. Both have a delicate one 

 above the diapophyses in front, the T. grandaevus behind also. There 

 is no posterior zj-gapophysis in the T. galli. The caudal of the latter 

 is also relatively shorter. 



Length centrum 2 in. (50 mm.) 



Depth articular face anterior 1 in., 5.7 lines (11.4 mm.) 



Width articular face anterior 1 in., 7 I'nes (1-1 mm.)'' 



