F. B. Zoomis — JVew Mosasaur from the Ft. Pierre. 555 



Art. XXXYII. — A New Mosasanr from the Ft. Pierre ; 

 by F. B. Loomis. 



Just west of the Black Hills in Wyoming there stretches 

 from southeast to northwest a great belt of black shales of the 

 Ft. Pierre age. The scarcity in them of both invertebrate and 

 vertebrate fossils has caused these beds to be neglected, not to 

 say shunned ; for the abundance of alkali in the shales makes 

 camping in the region a dubious pleasure, However on the 

 high ground west of Edgemont, near the heads of the small 

 streams, some vertebrates have been found, the first by the 

 American Museum of Natural History, which however were in 

 such hard concretions as to make their preparation and study 

 impractical, and again by the Amherst College expedition of 

 1903, these latter being in the shales and in a fair state of pre- 

 servation. This collection was made at the head of Mule 

 Creek, 20 miles due west of Edgemont, and contains a fair 

 fauna of both invertebrates and vertebrates, the most interest- 

 ing of which is a set of mosasaur bones belonging to a new 

 species and represented by practically all parts of the skele- 

 ton. 



The invertebrates occurred in concretions at the same local- 

 ity and horizon and are useful in determining the age of the 

 horizon. I give the list of shells found which are typically 

 Ft. Pierre species : 



Inoceramus sagensis var. nebras- Protocardia rara E & S 



censis Owen Callista deweyi M & H 



Inoceramus crispii var. barba- Callista peplucida M & H 



bini Morton Anisomyon subovulatus M & H 



Yoldia ventricosa M & H Entalis ? paupercula M & H 



Nuculana ? equilateralis M & H Vanikoro ambigua M & H 



Pteria linguiformis E & S Aporrhais biangulata M & H 



Pteria nebrascana E & S Fasciolaria ? flexicostata M & H 



Chlamys nebrascensis M & H Heteroceras ? cochleatum M & H 

 Syncyclonema rigida M & H 



Beside the invertebrates there occurred a series of verte- 

 brates which in their generic features resemble a Niobrara 

 fauna, but they are specifically different though the preserva- 

 tion is not sufficiently good to use them to make new species. 

 In their preservation there was some crushing, and the cracks 

 filled with gypsum, later expanding so that delicate bones are 

 usually distorted and very difficult of preparation. 



