280 SYSTEMATIC PALEONTOLOGY 



Occurrence. MARTINSBURG SHALE (Eden division). Jordans Knob, 

 one and one-half miles northeast of Fort Loudon, Pennsylvania. Eden 

 shale at Cincinnati, Ohio. 



Collection. IT. S. National Museum. 



Family LEDIDAE 



Genus CLIDOPHORUS Hall 



CLIDOPHORUS PLANULATUS (Conrad) 



Plate LIV, Fig. 37 



Nuculites planulata Conrad, 1841, 5th Ann. Rept. New York Geol. Surv., 



p. 50. 

 Cleidophorus planulatus Hall, 1847, Pal. New York, vol. i, p. 300, pi. Ixxxii, 



figs. 9a-e. 



Description. " Shell transversely elliptical oblong, height about half 

 the length of the shell, with the beak approximately a third of the length 

 of the shell from the anterior end. Umbonal ridge low, distinctly defined 

 along its cardinal border where it makes an angle of 162 to 165 degrees 

 with the longitudinal axis of the shell. Above this umbonal ridge, the 

 posterior cardinal slope of the shell is flattened and subalate. The pos- 

 terior part of the hinge-line extends from the beak for a distance equalling 

 about two-fifths the length of the shell, and then makes an angle of about 

 150 degrees with the posterior margin of the shell. The margin is rather 

 strongly rounded at both the posterior -and anterior ends of the shell, the 

 maximum 'curvature of the anterior margin, however, being nearer the 

 hinge-line. The basal margin is moderately and evenly convex. The 

 clavicular adductor support anterior to the beak forms an angle of about 

 80 degrees with the longitudinal axis of the shell; it is comparatively 

 straight and extends downward to about the middle height of the shell ; it 

 is sharp and narrow, appearing on the cast of the interior of the shell as a 

 sharp incision not depressing the immediately adjoining part of the shell. 

 The convexity of the shell is moderate, that of a shell 9 mm. in height 

 being about 1.6 mm. Specimens 20 mm. in length occur." Foerste, 1914. 



