98 Annals of the Carnegie Museum. 



covered by a strong deltidial callosity. Crenulations on the interior 

 margin are oblique, diverging from the beak, extending from the fora- 

 men less than half way to the cardinal angles. Surface marked by 

 strong, large radiating striee alternating with four or five smaller striae 

 and increasing by implantation" (Eleventh Annual Report Indiana 

 State (Geological Survey, 1881, p. 289). Here then there are examples 

 of four of Hall and Clarke's subdivisions ; Brachyprion, Leptostrophia, 

 Pholidostrophia, and Stropheodonta (S. demissa type) which agree 

 in internal structure but have great variation in external ornamentation. 

 These facts would seem to indicate that the name Pholidostrophia 

 should be given the same taxonomic value as the names Brachyioprion 

 and Leptostrophia, instead of being raised to generic rank. 



TJie Same Species from 0/her Localities. 



Specimens from East Bethany, N. Y., are of about the same size as 

 the Canandaigua Lake specimens, but are somewhat wider in propor- 

 tion to the length. The index is from 1.39 to 1.49 mm. 



From Eighteen Mile Creek there are numerous specimens, most of 

 which are smaller than the largest ones in the present collection. 

 The smallest is 8 x 10 mm. and the largest 12x17 mm. An average 

 specimen is 10. 5 x 14 nim. Most of the specimens have their cardinal 

 extremities more or less extended. One specimen that is 14 mm. 

 wide below the hinge, measures 18.5 mm. along the hinge. Another 

 14 mm. in width below, is 17 mm. on the hinge. These specimens 

 are only moderately convex and have not yet reached the stage when 

 they are sharply deflected in front. One of the specimens shows in- 

 distinctly a few distant, radiating strire. 



Very similar to these, but with a slightly lower index, are the speci- 

 mens from Thedford, Ontario. These specimens are very uniform in 

 size. The largest is 11. 5 x 15 mm. and the smallest 10 x i3-5 "im. 

 The index is 1.30 to 1.35 mm. 



Notes on Other Species of Stropheodonta. 

 S. concava Hall. 



Hall, Pal. N. Y., IV, 1867, p. 96, pi. 16, figs. 12 and 15. 



One well preserved dorsal valve shows the character of the muscle 

 scars in this species. The adductor scars are large, broadly oval, and 

 separated by a median depression in place of the usual septum. The 



