144 PROCEEDINGS OF THE NATIONAL MUSEUM vol. m 



of posterior teeth variable, but wider anteroposteriorly in proportion 

 to height; some have a fairly large accessory cusp with denticulated 

 cutting edge at base posteriorly, others have three or more tubercules, 

 one above the other, and many have a rugose or coarsely sculptured 

 internal face. 



Basihyal almost hexagonal; thyrohyals dilated beyond basal con- 

 striction and tapering toward extremity; stylohyal somewhat flattened 

 and curved slightly from end to end; olecranon process of ulna elon- 

 gated, with deep notch between it and shaft; dorsal and lumbar 

 vertebrae characterized by high neural canals, 



Tretosphys gabbii (Cope) 



Plates 17-21 



Delphinapterus gabbii Cope, Proc. Acad. Nat. Sci. Philadelphia, vol. 20, p. 191, 



1868. 

 T[retosphys] gabbii Cope, Proc. Acad. Nat. Sci. Philadelphia, vol. 20, p. 191, 1868. 



Type specimen (USNM 11234) : An imperfectly preserved anterior 

 caudal vertebra that lacks the neural spine and transverse processes. 

 Collector, James T. Thomas. 



Measurements of type specimen (Case, 1904, p. 9) 



Anteroposterior diameter of centrum 52. 6 mm. 



Transverse diameter of anterior face of centrum 40. 7 



Vertical diameter of anterior face of centrum 37. 4 

 Transverse diameter of neural canal at base 4. 3 



Horizon and locality: Probably excavated by slaves of Dr. 

 Thomas in marl bed on De la Brooke estate, about 1 mile east of 

 Patuxent, Charles County, Md. Calvert formation, upper Miocene. 



Referred specimen (USNM 10709): Ankylosed symphysis of 

 mandibles, length 170 mm.; section of the left mandible posterior to 

 symphysis, with 3 teeth, length 66 mm.; section of right maxillary, 

 with 3 teeth, length 138.5 mm.; 2 pieces of premaxillary; 54 detached 

 teeth; basihyal, left thyrohyal, and incomplete left stylohyal; fourth 

 dorsal and an anterior lumbar vertebrae; left ulna; proximal end of 

 radius; 1 carpal; 1 phalange; and 4 rib fragments. Collector, Dr. 

 Rodney B. Harvey, June 23, 1918. 



Horizon and locality: In a yellowish white diatomite with con- 

 siderable content of fine grained sand, presumably referable to Zone 

 5, about six feet above the oyster (Ostrea percrassa) layer, one-half 

 mile south of old Chesapeake Beach wharf (and 135 yards south of 

 Marinelli's place), Calvert County, Md. Among the diatoms recog- 

 nized by Paul S. Conger in the matrix are: Coscinodiscus obscurus A. 

 Schmidt, Coscinodiscus levnsianus Greville, Coscinodiscus perforatus 

 Ehrenberg, Actinoptychus undulatus (Bailey?), Actinocyclus monili- 



