82 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 78 



the mesial depression is less conspicuous in that species, and this, 

 together with obvious differences in outline and size, preclude the 

 possibility of specific identity. As to their generic relations there 

 is less certainty. 



Occurrence. — Bright Angel shale just above lower massive sand- 

 stone, near mouth of Bass Canyon, Grand Canyon of the Colorado, 

 Ariz. 



Holotype. —C&t. No. 56463, U.S.N.M. 



DOUBTFUL SPECIES 



INDIANA ? ACADICA (Matthew) 



Plate 9, Figure 13 



Primitia acadica Matthew, Trans. Royal Soc. Canada, vol. 3, sec. 4, 1886, 

 p. 66, pi. 6, figs. 22, 22a, b; Trans. New York Acad. Sci., vol. 15, 1896, p. 

 196, pi. 15, figs. 5a-c. 



This species is known only from the imperfect specimen first de- 

 scribed and figured by Matthew, as noted above, in 1886. An exami- 

 nation of this specimen, which was loaned by the University of Toronto 

 with the other types of bivalved Crustacea described by Matthew, 

 shows that it is in good condition except for a strip along the hinge 

 which is broken away. The outline seems to have been somewhat 

 elongate elliptical, the surface rather strongly convex, the edge 

 rounded inward, and the test thin, noncalcareous, poUshed, and dis- 

 tinctly punctated. These features remove the species from Primitia 

 and point strongly to Indiana. Further, assuming that the missing 

 part is only that immediately adjacent to the hinge line, it is inferred 

 that the specimen is a left valve of a species of this genus closely 

 allied to I. secunda, I. dermatoides, and /. suberecta. A perfect speci- 

 men might possibly prove identical with one of these species, but so 

 far as it goes, the imperfect type of I.f acadica can not be exactly 

 correlated with the supposed corresponding parts of any described 

 species. Still, it should be confessed that this assertion is based 

 chiefly on the conviction that the part missing from the specimen 

 is not, as Matthew thought, merely the antero-cardinal part, but that 

 it includes the whole of a short hinge, and that the line of fracture is 

 approximately parallel to the removed dorsal edge. If this supposi- 

 tion is correct, then the species must be one of the strongly oblique 

 forms with a broadly rounded posterior margin, like /. dermatoides 

 and I. suberecta. In the matter of size, I.? acadica agrees much better 

 with I. secunda than with the other species referred to in these 

 remarks. 



As the injury to the type specimen has removed the back and 

 cardinal angles, which parts afford the most diagnostic specific char- 

 acters of Indiana and allied genera, it may never be possible to iden- 

 tify the species beyond question. However, a feature not observed 



