AET. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 79 



INDIANA LABIOSA, new species 



Plate 9, Figures 26, 27 



Description. — Carapace exceeding the average in size, rather elon- 

 gate subelhptical in outline, but shghtly oblique, dorsal edge straight, 

 fully two-thirds as long as the greatest length of carapace; dorsal 

 angles well defined, the anterior sharper than the posterior; ends 

 subequal, rounded, the posterior extending a trifle farther beyond the 

 dorsal angle than does the anterior; ventral part of outUne moder- 

 ately convex, somewhat produced and obtusely angular near the 

 middle. Surface of valves moderately convex, originally probably well 

 rounded, in the present compressed condition appearing somewhat 

 flattened in the median portion and relatively steep adjacent to the 

 margin; ventral margin with a distinctly flattened rim becoming 

 gradually obsolete as it passes round the ends. Test mostly destroyed 

 by solution, the delicate remnants along the dorsal and ventral edges 

 black; surface markings unknown. 



Dimensions: Length 5.8 mm., greatest height, including ventral 

 border, 4.0 mm,, excluding border 3.6 mm., thickness of right valve 

 1,0 mm. or more. 



Remarks. — The broad flattened ventral rim gives this species an 

 aspect not shared by any other of the genus known. In general 

 form it is greatly like Matthew's figure of his Leperditiaf primaeva 

 but somew^iat less in accord with the specimens tentatively referred 

 to that species under the name Indiana primaeva. I. labiosa differs 

 from both in being larger and relatively more elongate besides having 

 a flat border unhke anything seen in /. primaeva. The two species 

 from the Bright Angel shale next described are probably its closest 

 known allies. The reader is referred to the remarks following the 

 descriptions of those species for detailed comparisons. 



Occurrence. — Middle Cambrian, Stephen formation, in bed 2d of 

 Walcott's section at Mount Bosworth, British Columbia,^ 



Cotypes.— Cat. No. 56464, U.S.N.M. 



INDIANA FABA, new species 



Plate 5, Figures 10-14 



Description. — Carapace of medium size, subovate, moderately in- 

 equilateral; hinge straight, about two-thirds as long as the greatest 

 diameter, its extremities sharply defined in the dorsal angles; ends 

 subequal, the posterior the more produced and more strongly rounded 

 in its lower hah than the anterior; ventral margin rather strongly 

 convex. Surface of valves A\ithout nodes, moderately convex, the 

 point of greatest elevation in front of the middle; without a flattened 



'See Smithsonian Miscellaneous Collections, No. 1812, p. 211. 



