TkopiDOLHiTUS Fai'xa AT Canandakjua T.ake, N. Y. 131 



East Bethany are of larger size, have a higher index, and show a 

 greater number of senile individuals. 



The individuals from Ludlowville have, in the adult condition, the 

 width of the hinge about equal to the width below, and most of them 

 have the length nearly equal to the width, thus giving a low aver- 

 age index. The lowest index was 1.07 and the highest 1.33. The 

 average of ten adults is 1.17. The largest specimen was 22 mm. 

 long and 25 mm. wide. A single specimen showed, on one margin, 

 two plications which had bifurcated in front of the last growth line. 

 This is an unusual condition, although Hall figures a senile individual 

 which has all the plications of the dorsal valve bifurcated in front. 

 (Pal. N. v., Vol. IV, pi. 62, Fig. 3^.) 



The specimes from York are small. The largest one is only 19 mm. 

 long and 22.4 mm. in width. The index, average often specimens, 

 is I. 2 1 . The range is 1.09 to 1.29. 



In the collection from Eighteen Mile Creek there are specimens 

 from ;^.8 mm. by 3.2 mm. up to 20.4 x 25 mm. The index varies 

 from .84 to 1.30, and the average often adults is 1.22. The mature 

 specimens retain a neanic character in having the median plication of 

 the ventral valve only a little stronger than the neighboring ones. 

 Many individuals have the strong angular type of plications. 



From East Bethany there are numerous specimens ranging from 

 II X 13 mm. to 27 X 37 mm. The index varies from 1.13 to 1.44 

 and the average for thirty-five specimens is 1.27. Of the 510 

 specimens examined, nineteen per cent, showed senile characters. 

 These individuals are mainly larger than the average adults, but the 

 index has almost identically the same range as in the adults, viz. 1.13 

 to 1.44 as compared with 1.13 to 1.42. There are in the collection 

 from this place no distinct varieties, but the long forms, 22 x 25 

 mm., index T.13, grade by numerous intermediate steps into the wide 

 forms, 19 X 27 mm. index 1.42. The number of plications varies 

 from 17 to 28. There are only a few specimens from Moscow, but 

 they agree in i)ro])ortion and form with those from East Bethany. 

 The average of the indices is 1.24. The largest specimen is 26 X 32 

 mm. 



The facts would seem to indicate that, while the conditions at Can- 

 andaigua Lake were favorable for the production of large numbers of 

 individuals of this species, they were not such as to allow them to 

 reach the maximum development possible before the senile stage of 

 their lives. 



