ART 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 75 



gula, but that species is readily separated by its more narrowly 

 rounded posterior extremity and more uniformly rounded postdorsal 

 edges. It is also allied to the associated /. dermatoides, but the 

 punctation of its test is more minute and more crowded, and when 

 properly oriented the shape of the valves is quite different. 



Occurrence. — Lower Cambrian, limestone outcropping on Reid's 

 farm, IK miles north of Bald Mountain, Greenwich Township, 

 Washington County, N. Y. 



Holoty pe.— C&t. No. 56469, U.S.N.M. 



INDIANA DERMATOIDES (Walcott) 



Plate 9, Figures 16, 17 



Leperdiiia dermatoides Walcott, Amer. Journ. Sci., ser. 3, vol. 34, 1887, p. 192, 

 pi. 1, figs. 13, 13a; 10th Ann. Rep. U. S. Geol. Surv., 1890, p. 626, pi. 80, 

 figs. 1, la. — Matthew, Amer. Geol., vol. 8, 1891, p. 290. — Cobbold, Quart. 

 Journ. Geol. Soc, vol. 76, 1921, p. 368. 



Indiana dermatoides Chapman, Proc. Royal Soc. Victoria, new ser., vol. 31, 1918, 

 p. 109. 



Description. — Carapace of medium size, subelliptical in outline, the 

 ellipse obliquely truncated along the hinge line; dorsal angles distinct, 

 the anterior about 100°, the posterior about 135°; hinge less than half 

 the total length of carapace, constructed seemingly so that in its 

 posterior half the edges of the opposite valves overlap; anterior end 

 narrow, the outer margin curved gently and so that its most promi- 

 nent point projects but slightly beyond the dorsal angle; ventral part 

 of outline moderately convex, trending obliquely backward toward 

 the posterior extremity, around which the outline continues with a 

 semicircular curve; upper third of posterior margin nearly straight. 

 Valves moderateh^ convex, liighest in the posterior half, the slope 

 near the antero-dorsal half rather more abrupt than elsew^here; ap- 

 parently without a flattened rim. Test thin, black, distinctly punc- 

 tate; punctae rather closely arranged. 



Dimensions of left valve (original type of species) : Greatest length 

 5.9 mm., length of hinge line 3.1 mm., distance from middle of ventral 

 edge to postdorsal angle 3.3 mm., thickness about 1.3 mm. 



Remarks. — The original collections used by Doctor Walcott in de- 

 scribing this well-marked species proved to contain at least two 

 distinct forms, the second being now referred to /. secunda (Matthew). 

 Other specimens of the original lot are either too imperfect or insuf- 

 ficiently prepared to admit of definite classification. A third species, 

 /. suberecta of this vvork, does occur in the same bed, and it is there- 

 fore not improbable that it also is represented among the undeter- 

 mined specimens. 



Critically compared with the other species of Indiana, I. derma- 

 toides appears more or less closely allied to I. secunda, I. pyrijormis, 



