MAEYLAXD GEOLOGICAL SURVEY 73 



Family MYLIOBATIDAE MUller and Henle. 



Genus MYLIOBATIS Cuvier. 



The best account of the dentition of this genus, with valuable sugges- 

 tions for the determination of fossil teeth, is given by A. S. Woodward.' 

 The development of young teeth has also deen studied by Jaekel/ and 

 the dentition of some hitherto misunderstood fossil forms correctly 

 interpreted by him. 



It is stated in the report on the Eocene of Maryland, pp. 264 and 

 265, that the " anterior end " of the large dental pavement of Myliohatis 

 ivagkier Leidy is shown uppermost in the figures, but as these were inad- 

 vertently turned upside down, the statement should be amended so as 

 to read posterior end. In most cases the orientation of Myliol)atid 

 dental plates can be readily determined. Traces of wear, due to the 

 comminution of food during life, occur always at the anterior end ; the 

 transverse sutures of the median teeth are usually curved posteriorly 

 along the lateral margins; and the superficial striae or wrinkels (when 

 the gano-dentine layer is unabraded) always radiate outwards on passing 

 from front to back. A longitudinal section shows that the median teeth 

 are not only closely appressed against one another throughout their 

 height, but they overlap in a tectiform manner, each tooth sloping 

 obliquely backward. 



Two species of Myliohatis have been described by Cope from the 

 Eocene marls of New Jersey, which seem to have escaped general notice. 

 These are M. glottoides ' and M. redidens.' M. serratus Leidy, founded 

 on much abraded teeth from the same horizon and locality, is renamed 

 M. leidyi by 0. P. Hay,* the former specific title being preoccupied. 



Myliobatis gigas Cope. 

 Plate XXVIII, Figs. 3a, 3b; Plate XXIX, Figs, la, lb. 



Myliohatis gigas Cope, 18fi7, Proc. Acad. Nat. Sci. Phila., vol. xix, p. 140. 

 Myliobatis vicomicanus Cope, 1867, Proc. Acad. Nat. Sci. Phila., vol. xix, p. 140. 



'Ann. Mag. Nat. Hist. [6], vol. i, (1888) pp. 86-47; Proc. Geol. Assoc, vol \vi 

 (1899), p. 3. 



2 Die eocanen Selachier vom Monte Bolca, pp. 129-131, and 1.50-159. Berlin, 1894. 



3 Proc. Amer. Pbilos. Soc, vol. xi, 1870, pp. 393, 394. 

 ■•Arner. Nat., vol. xxxiv, 1899, p. 78.5. 



