100 SYSTEMATIC PALEONTOLOGY 



Dental pavements are not imcommon showing as many as nine longi- 

 tudinal series of median teeth intact (Plate XIII, Figs. 6, 7). One of 

 the largest npper dental plates examined is from the Aquia Formation 

 of Potomac Creek, and in this the median teeth are 6.5 cm. wide, 1.5 cm, 

 long, and 3 cm. thick, not inclnding the root. The antero-posterior 

 curvature of the coronal surface is so great as to form a nearly perfect 

 semicircle, having a diameter of 8 cm. and a periphery of over 13 cm. 

 Nine of the median teeth are preserved in regular series, together with 

 a portion of the lateral series on both sides. There is considerable re- 

 semblance between this species and M. holmesii from the Eocene of 

 South Carolina. 



The type consists of fragmentary dental plates of the upper and lower 

 jaws. 



Occurrence. — Nanjemoy Fokmation. Woodstock. Aquia Foema- 

 TION. Clifton Beach, Liverpool Point, Aquia Creek, Potomac Creek. 



Collections. — Johns Hopkins Universitj^, Marjdand Geological Survey. 



Myliobatis magistee Leidy. 

 Plate XII, Fig. 3; Plate XIII, Figs, la, lb. 



Myliobalis magister Leidy, 1876. Proc. Acad. Nat. Sci. Phila., p. 86. 



Myliohatis magister Leidy, 1877. Jour. Acad. Nat. Sci. Phila., N. S., vol. viii, p. 



233, pL xxxiii, fig. 7. 

 Myliobatis holrnesii Woodward, 1899. Cat. Foss. Fishes, Brit. Mus., pt. i, p. 122. 



Description. — Dentition very large and massive, the median teeth at 

 least six times wider than long, their sutures curved backward near the 

 lateral margins, and sometimes very faintly so in the central area. 

 Coronal contour of upper dental plate uniformly arched from side to 

 side, and also to an equal extent in a longitudinal direction; lower dental 

 plate less curved antero-posteriorly than the upper, and slightly de- 

 pressed along the median line. Surface smooth when unworn, or with 

 fine superficial striae slightly convergent toward the front. 



This gigantic species, which is exceeded in size only by the Egyptian 

 M. penioni, is not actually known to occur in Maryland, being confined, 

 so far as known, to tlie P^ocene Phosphate Beds of South Carolina. It 

 is noticed in this connection, however, because of the interest attached 



