ELASMOBRANCHII. 101 



vex. Enamel surface broad, depressed or usually more or less 

 flattened, and edges of front teeth at least varying more or less 

 convex. Greatest width or vertical diameter of enameled surface 

 usually uniform, and about one-fourth in entire horizontal diam- 

 ater. Root low, greatly depressed, greatly inclined backward, so 

 that beginning of lower level surface is about opposite medial 

 lesser diameter of enameled surface. Posterior part of root al- 

 ways seen projecting a little more or less for slight distance behind 

 enameled surface as latter is viewed from above. Entire surface 

 of root marked with moderately numerous sutures, all parallel, 

 and most distinct behind. Front edge of enamel surface curves 

 slightly convexly over root, leaving a slight longitudinal groove 

 below. Posterior edge just below enamel with a slight longi- 

 tudinal ridge. Length (greatest breadth) 40 mm. Here de- 

 scribed from examples from the Maryland Miocene. 



Known only from the dental plates. 



Formation and locality. I have not examined any examples 

 from New Jersey where it has been ascribed to the Miocene. 

 Cope originally had a single example and I do not think any 

 others have been recorded from the State since [Shiloh marl, 

 Kirkwood formation, Miocene, K.]. 



Genus RHINOPTERA Cuvier. 



Rhinoptera (Kuhl) Cuvier, Regne Animal, Ed. 2, II, 1828, p. 401. Type 

 Myliobatis marginata G. St. Hilaire, first species, restricted by Bonaparte, 

 Nuov. Ann. Sci. Nat. Bologna, II, 1838, p. 201. 



Zy'gobatis Agassiz, Poiss. Foss., Ill, 1843, P- 79- Type Myliobatis jussieui 

 Cuvier, virtually monotypic. 



Zygobates, auct. 



Trikeras Harless, Abh. N. Phys. Class., V, 1850, p. 841. No species given. 



Mylorhina Gill, Ann. Lye. Nat. Hist. N. Y., 1865, p. 136. Type Rhinoptera 

 lalandii Midler and Henle, designated, monotypic. 



Micromesus Gill, 1. c. Type Rhinoptera adspersa Miiller and Henle, desig- 

 nated, monotypic. 



Trycera (Koch) Doderlein, Man. I. Med., Ill, 1885, p. 242. Type Trycera 

 typica Koch (= Myliobatis marginata G. St. Hilaire), nom. in syn. 



This genus resembles Myliobatis in its dentition, having the 

 teeth in several series, the median being very broad. It differs, 

 however, in the emarginated muzzle and having the cephalic fins 

 below the level of the disk. 



