MAETLAND GEOLOGICAL SURVEY 75 



is 8 cm. and the width of the largest tooth 6 cm. The extreme length 

 of the upper dental pavement measured in a straight line antero- 

 posteriorly is rather more than 10 cm. or along the arc of its curved 

 surface 12 cm. Its largest median tooth has a width of 8 cm. and a 

 length of 1.1 cm. 



Occurrence. — Calveet FoEiiATiox. Charles county near the Patux- 

 ent river. 



Collection. — Philadelphia Academy of Xatural Sciences. 



Myliobatis pachyodox Cope. 

 Plate XXIX, Figs. 2a, 2b. 



Myliobatis pachyodon Cope, 1867, Proc. Acad. Nat. Sci. Pbila., voL xix, p. 140. 

 Myliobatis pachyodon Leidy, 1877, Jour. Acad. Nat. Sci. Phila., 3ud ser., voL viii, 

 p. 343, pL xxxii. tig. 6. 



Description. — Dentition large and massive, the median teetli l)eing 

 unusually thick in proportion to their size. Except as regards thick- 

 ness, the median teeth are shaped similarly to those of M. gigas Cope 

 and the transverse sutures are similarly curved. The species is inter- 

 mediate in character between the accompanying M. gigas and M. magis- 

 ter from the Eocene, the latter having longer median teeth and more 

 strongly curved transverse sutures. The type of the present species, 

 which appears to be unique, exhibits only the left half of four anterior 

 median teeth and portions of three elongate lateral teeth. The median 

 teeth have a length of 1.1 cm. and thickness of 2.1 cm. If, as indicated 

 by the cross-section and longitudinal striae, the pavement is preserved 

 for rather more than one-half its width, the median teeth must have 

 been at least 6 cm. wide. 



Occurrence. — Calveet Foemation. Charles county near the Patux- 

 ent river. 



Collection. — Philadelphia Academy of Xatural Sciences. 



Myliobatis feangens n. sp. 

 Plate XXIX, Fig. 3. 



Myliobatis sp. Leidy, 1877, Jour. Acad. Nat. Sci. Phila., 3nd ser., vol. viii, p. 243, 

 pi. xxxii, figs. 7, 7a. 



Description. — Lower dental pavement nearly flat and relatively very 

 thin, in cross-section resembling M. gigas Cope. Median teeth about 



