160 NEW YORK STATE MUSEUM 



vexity of the opposite valve. The interior is not well shown. 

 The surface bears fine rounded or subangular plications, which 

 increase by bifurcation and intercalation till there are 11 or 12 

 in the space of 3 mm on the margin of the shell. Frequently 

 two of these are stronger just below the beak and form the begin- 

 ning of the sinus when one is present. They are crossed by fine 

 concentric striae. There are two or three strong upward curv- 

 ing spines, and sometimes the base of a fourth on each side of 

 the beak. Dimensions of specimens of average and extreme size 

 are: 1) length 7 mm, width 9 mm; 2) length 9.6 mini, width 

 12.2 mm. 



These specimens differ from C h o n e t e s 1 i n e a t u s of the 

 Onondaga limestone in being larger, less convex, and in the 

 number and size of the cardinal spines. 



Though the greater size, less convexity, and occasional pres- 

 ence of a sinus seem features of sufficient importance to con- 

 stitute a new species, they are not always associated in the same 

 specimen, and there are moreover shells which appear to form a 

 gradation from the most extreme to the more typical specimens. 



strophalosia King 

 Strophaiosia truncata (Hall) 



Pal. N. Y. 4:160, pi. 23 



In beds A, B, and C, of the lower shales this species is small 

 and comparatively rare, but in the upper shaly part of bed D it 

 is extremely abundant and of greater size. Individuals measur- 

 ing 8.6 mm in length, 11.4 mm in width, and with the truncation 

 occupying about one sixth the area of the pedicle valve are com- 

 mon. In bed I they are small, extremely gibbous, and with the 

 truncation occupying about one third the area of the valve. An 

 average specimen measures: length 4.6 mm; width 5 mm; con- 

 vexity 1.9 mm. 



In beds II, III, and IV, the specimens are larger, the area of 

 the truncation decreasing in proportion to the increase in the 

 size of the shells. The following measurements of the largest 

 specimens observed from beds I, II, and IV, serve to illustrate 



