288 SYSTEMATIC PALEONTOLOGY 



Genus MODIOLODON Ulrich 



MODIOLODON TRUNCATUS (Hall) 



Plate LVII, Fig. 25 



Modiolopsis truncatus Hall, 1847, Pal. New York, vol. i, p. 296, pi. Ixxxi, 



figs. 3a, b. 

 Modiolopsis truncatus Hall and Whitfield, 1875, Geol. Surv. Ohio, Pal., 



vol. ii, p. 86, pi. ii, fig. 13. 

 Modiolodon truncatus Ulrich, 1893, Geol. Surv. Ohio, vol. vii, p. 656, pi. Ii, 



figs. 9, 10. 



Description. " Shell below the medium size ; shortly ovate in outline, 

 the widest part being about one-third of the entire length from the 

 posterior end. Valves compressed, or depressed convex, most prominent 

 near the center. Beaks small and closely compressed, scarcely projecting 

 beyond the line of the hinge. Anterior margin rather shortly rounded, 

 the extremity extending but little beyond the beaks ; basal margin gently 

 and regularly curving; posterior end more broadly rounded than the 

 anterior and most abruptly at the postero-basal portion; above, it slopes 

 more gradually backwards to the extremity of the hinge line, with which 

 it unites without forming any perceptible angle. 



" Surface of the valves marked by irregular, rather strong, concentric 

 lines of growth. 



" The internal casts the condition in which the species is usually 

 found in the softer parts of the formation show a large, elongate pos- 

 terior muscular scar, situated a little within the postero-cardinal margin, 

 and parallel with it; also a smaller lunate anterior scar, and an entire 

 pallial line." Hall and Whitfield, 1875. 



Occurrence. MARTINSBURG SHALE (Fairview division). Tuscarora 

 Mountain, one and one-half miles southeast of McConnellsburg, Pennsyl- 

 vania. Pulaski shale near Eome, New York. 



Collection. U. S. National Museum-. 



