Apr. 1903. NORTH AMERICAN PLESIOSAURS—WILLISTON. Il 
Wyoming. The processes are attached. The description will apply 
to caudal vertebre of various genera. 
URQNAUTES. 
Mu per LOC. ACH Nato ein Pile t O7Os34 5. 
CETIFORMIS Cope, l. c. 346.—Fort Pierre (?) Cretaceous, Montana. 
SPECIES Cope, Amer. Nat. 1887, 566.—Fox Hills Cretaceous, New 
Mexico. 
This genus was based upon cervical, dorsal and caudal vertebre. 
The cervicals are short, with the processes partly attached, and the 
ribs single-headed. 
Professor Cope referred the type species to the Fox Hills Cre- 
taceous with doubt. I suspect, rather, that the horizon is Fort 
Pierre. 3 ; 
OROPHOSAURUS. 
Cope, Amer. Naturalist, 1887, 564. 
PAUCIPORUS Cope, l. c.—Fox Hulls Cretaceous of New Mexico. 
Based upon parts of three cervical vertebrae. The neural arches 
are coéssified, the ribs free. Centra short; ribs single-headed. 
PIPTOMERUS. 
Cope, Amer. Nat. 1867, 564. 
MEGALOPORUS Cope, I. é. 564.—Fox Hills Cretaceous, New: Mexico. 
MICROPORUS Cope, |. c.—Fox Hills Cretaceous, New Mexico. 
HEXAGONUS Cope, |. c.—Fox Hills Cretaceous, New Mexico. 
This genus and species ‘are based upon cervical and dorsal verte- 
bre only. The cervicals are short, the processes free and the ribs 
single-headed. 
TRINACROMERUM. 
Cragin, Amer. Geologist, Dec. 1888. 
*BENTONIANUM Cragin, |. c.; ibid, 1891, 171.—Benton Cretaceous, 
Kansas. 
A large part of the skeleton was known to the describer, includ- 
ing the skull, vertebra, part of the girdles and limbs. 
