7^ SYSTEMATIC PALEONTOLOGY 



localities. The teeth of these genera are sufficiently distinctive, but in 

 the case of their dermal armor, including caudal spines, the determina- 

 tions are necessarily very doubtful. 



Eaja (?) DUX Cope. 

 Plate XXVIII, Fig. 2. 



Raja dux Cope, 1867, Proc. Acad. Nat. Sci. Phila., voL xix, p. 141. 



Description. — This " species " was founded by Cope on a large and 

 much abraded dermal tubercle from Charles county, the original de- 

 scription of which is as follows: 



" This species is represented by a dermal plate, which was originally 

 covered by enamel, and probably supported a spine; the latter, and a 

 considerable portion of the former, have been lost. The form is un- 

 symmetrically subpentagonal, longer than broad. One extremity trun- 

 cate, the other obtusely narrowed. Inferior surface concave-flattened; 

 superior rising to a small median plane, edges thin. Greatest elevation 

 near the narrow extremity, where the spine stood; a groove extends 

 from the position of the latter to the margin. Surface indistinctly 

 ribbed at right angles to the margin. Enamel with slight wavy ribs, 

 those near the centre much coarser than those near the circumference. 

 Length of plate 15 lines; greatest width 12.75 lines; greatest depth 4 

 lines. A second plate, perhaps of the same species, differs in its 

 narrower form; it is without enamel. This ray was larger than any 

 described from the European Tertiary." 



The type-specimen, of which a figure is given in the present volume 

 for the first time, is preserved in the Museum of the Philadelphia 

 Academy of Xatural Sciences. Similar but smaller dermal tubercles 

 from the Miocene of Wurtemberg are assigned by various authors ' to 

 the genera Raja, Trygon, Acantliohatis and even Acipenser. 



Occurrence. — Calvert Formatiox, Charles county near the Patux- 

 ent river. 



Collection. — Philadelphia Academy of Natural Sciences. 



'J. Probst, Beitiage zur Kenntniss der fossilen Fische aus der Molasse von Bal- 

 tringen (Wiirtt. Jahresb., vol. xxxiii, 1877, pp. 97-99, pL ii). — O. Jaekel, Ueber ter- 

 tiare Trygoniden (Zeit. d. deutsch. geoL Gesell., voL xlii, 1890, p. 365). — Idem, Die 

 eocanen Selachier Tom Monte Bolca, p. 140, Berlin, 1894. 



