Tropidoi-epius Fauxa at Caxandaigua Lakk, X. y. 91 



Cardinal Process. — The cardinal process is deeply bifurcate in tlie 

 youngest specimens showing it. In older stages each part is again 

 divided by a sharp depression which becomes deeper as development 

 goes on. On each side of the process are the dental lamella;, which, 

 in young specimens, are sharp and thin, but later become low and 

 rounded. In some adults they are hardly to be distinguished from the 

 two ridges which bound the posterior adductor scars. 



Tlie Same Species From Otiicr Localities. 



A single specimen from (ienessee, N. Y., is smaller than the ones 

 just described. It is i6 x 19 mm. and has 26 prominent striai, be- 

 tween which are fascicles of seven or eight small ones. This specimen 

 is quite regularly convex. 



There are several specimens from East Bethany in the collection, 

 all of which are small, but show mature characters. The largest speci- 

 men is 16 X 21 mm., and has 60 prominent stria; in front with 

 groups of three or four smaller ones between. The smallest is 

 8x 1 1.5 mm. and has 23 striae on the front. An average specimen 

 is 13 X 20 mm., with 50 prominent striae on the front, 9 of which 

 extend to the beak. Although the specimens are small they are 

 strongly convex, instead of being moderately convex or nearly flat, as 

 is the immature condition of the specimens from Canandaigua Lake. 



Stropheodonta perplana Conrad. (Plate III, Row i.) 



Hall, Pal. X. v., 1867, pp. 92, 98, pi. 11, fig. 22, pi. 12, figs. 13-15. 



There are, in the collection, about 150 nearly perfect specimens be- 

 longing to this species. The majority of them are separate valves, 

 more of the ventral than of the dorsal, and, as is the case with .S". iiicE- 

 qiiistriata, the pedicle vahe is the more perfectly preserved. A few 

 adult individuals retain both valves. The specimens range in size 

 from 1.6 X 1-8 mm. to 21 x 24 mm. All stages between these limits 

 are represented. On the beaks of both valves the younger stages are 

 well shown. 



A figure showing the deltidium, pedicle opening, and nepionic stage 

 of this species has been published by Beecher (Am. Jour. Sci., 3d 

 series, A^'ol. XLI, i8gi, p. 357, pi. 17, fig. 17). Hall has figured 

 specimens from the Corniferous, Hamilton and Chemung. (Jf these, 

 the smallest from the Corniferous is 15x19 mm., the largest 37 x 46 

 mm. The smallest from the Hamilton is 19x20.5 mm. and the 



