MARYLAND GEOLOGICAL SURVEY 369 



Occurrence. CHAMBERSBURG LIMESTONE (Tetradium cellulosum 

 bed) . Fort Loudon, Franklin County, Pennsylvania. The type specimens 

 were found in the Eysedorph conglomerate at Eysedorph Hill, Eensselaer 

 County, New York. 



Collection. U. S. National Museum. 



Genus CERATOPSIS Ulrich 



CERATOPSIS CHAMBERSI (Miller) 



Plate LV, Fig. 34 



Beyrichia chambersi Miller, 1874, Cincinnati Quart. Jour. Sci., vol. i, p. 234, 



fig. 27. 

 Beyrichia cham'bersi Hall and Whitfleld, 1875, Pal. Ohio, vol. ii, p. 104, 



pi. iv, figs. 11, 12. 

 Ceratopsis cham'bersi Ulrich, 1894, Geol. Minnesota, vol. iii, pt. 2, p. 676, 



pi. xlvii, figs. 19-22. 



Description. " Carapace minute, the extreme length not exceeding 

 half a line, and the greatest width not more than two-thirds as much as 

 the length. Form of the valves broad ovate, with one side, for a space 

 equal to about one-fourth of the width of the figure, cut away, forming 

 the straight hinge-line, which is equal in length to about six-sevenths of 

 the entire length of the carapace. Greatest width of the valve a little 

 more than one-third of the length from the anterior end. Surface of the 

 valves highly convex, most prominent near the middle of the length, 

 crossed by three curving sulci, none of which reach the ventral border, 

 the middle of the curve being directed towards the posterior extremity. 

 The middle sulcus is stronger and much deeper than the others, while the 

 posterior one is faintly marked, and situated at about the posterior third 

 of the length. The anterior sulcus is short, comparatively deep, nearly 

 semicircular, and situated within the anterior third of the length, and 

 about midway between the cardinal and basal borders. From the anterior 

 margin of this depression, or between it and the anterior border of the 

 valve, there rises a strong, thickened, lanceolate, or scythe-shaped, curved 

 spine, which equals in length two-fifths, or sometimes one-half that of 

 the entire valve. The anterior and posterior surfaces of the spine are 



