160 NEW YORK STATH MUSEUM 



vexity of ihv opposite valvo. The interior is not well shown. 

 The surface bears tine rounded or snbangular 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. Frecpieutly 

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

 ning of the sinus when one \s 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 mm; 2) length 9.6 mm, width 

 12.2 mm. 



These si)ecimens differ from Chonetes lineatus 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 

 si)ecimen, and there are moreover shells which appear to form a 

 gradation from the most extreme to the more typical specimens. 



sTROPHALosiA King 

 Strophalosia 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 gibbons, and with the 

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

 average specimen measures, loTiirth 4.6 mm: width .5 mm; con- 

 vexity 1.9 mm. 



In beds 'II, III, and IV, the sf>ecimens 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 



