338 



from any previously described, is indicated by a fossil submitted to my 

 examination l^y the Smithsonian Institution. The specimen was found by 

 Mr. Pearce in the Miocene formation of Gay Head, Martha's Vineyard. It 

 consists of a tooth represented in Fig. 7, Plate XXII, of the natural size. 



The form of the tooth, with its huge gibbous fang, led me at first to mis- 

 take it for that of a mosasauroid reptile, nor did I observe my error until it 

 was suggested by Professor Marsh 



The crown of the tooth is curved, conical, and without subdivisional planes 

 upon the surface. The inner and outer surfaces are barely defined i^ostero- 

 internally by a feeble and interrupted ridge. The enamel is singularly 

 wi-iukled, the wrinkles being short, vermicular, somewhat branched and 

 crowded, and they remind one of Arabic letters. At the base of the crown 

 the enamel is nearly smooth. The transverse section of the crown is cir- 

 cular, and measures 8 lines in diameter. The length of the crown when 

 complete appears to have been about twice the latter. 



The fang of the tooth, broken at the extremity, exposes to view a large 

 interior pulp cavity. It is longer than the crown and very gibbous. In its 

 relation of size and form, it is wonderfully like the corresponding part in the 

 teeth of Mosasaurus. It is ovoidal in tbrm and is curved in the dii'ection of 

 the crown. It is abruptly thickened at the base of the latter, and on one 

 side, near-the extremity, exhibits a deep groove. The texture of the fang, as 

 seen at its broken part, appears as dense as ordinary dentine. In the entire 

 condition, the fang has approximated 2 inches in length ; its diameter is 

 about half the length. 



REP T ILIA. 



Dinosauria. 



POICILOPLEURON. 



Deslongchamps : Mem. Soc. Liu. de Normandie VI, 1838, 37. 



POICILOPLEURON VALENS. 



Leidy : Pr. Ac. Nat. Sc. 1870, 3. 

 Antrodemus. Leidy : Ibidem, 4. 



Founded on several fragments of vertebree described page 267, and rep- 

 resented by Figs. 16 to 18, Plate XV, under the name of Antrodemus. 

 From Colorado, and supposed to have been derived from the Cretaceous 

 formation. 



