Troi'idolki'ius Fauna at C'ananhaicua I,akk, N. Y. 1.')9 



Mile Creek, N. \'., Thedford. Ontario, and Alpena, Michigan, were 

 selected from the rich collections of the Peabody Museum. 



With the other New York specimens the present material agrees in 

 general size and in number of plications. The largest of the speci- 

 mens from York measured 7.4 by 12 mm. and had 10 plications. 

 The height of the area of this specimen was .62 of the width of the 

 hinge. All the specimens from this locality had either 8 or 10 ])lica- 

 tions. The hinge width was equal to the width below, shorter, or, 

 in one case, slightly larger. A dorsal beak showed two stages of 

 growth, the smaller of which had only the fold developed and the 

 larger had four jjlications. In the smallest specimen, 4 x 6.2 mm., 

 the deltidial plates had coalesced over the lower third of the delthyrium. 



The Eighteen Mile Creek specimens showed much the same charac- 

 ters. The largest specimen was 7 x 10 mm. and had 8 plications. 

 The smallest was 3.8 X 5.4 mm. and had four plications. On this 

 specimen the deltidial plates were still separated. The width at the 

 hinge is always equal to, or less than, that below. 



About 200 well-preserved specimens from Thedford were examined. 

 Most of them are larger than the average of those from New York.' 

 The smallest specimen is 6.4 X 10 mm. and the largest is 11 X 22.4 

 mm., with 22 plications. The majority have from 12 to 18 plications. 

 In the smallest specimens the width of the hinge is about ecjual to the 

 greatest width below. In the larger ones it is almost invariably greater, 

 and the shell is frequently auriculate at the cardinal extremities. 



I'he areas of all the shells are inclined backwards and frequently 

 strongly curved and distorted. In no case was there any filling of the 

 pedicle opening by testaceous matter, even in the oldest shells. 



The shells from Alpena, Mich., resemble the Ontario specimens 

 more than they do those from New York State. They are large, 

 7 X 12 to 9.6 X 15.4 mm., and have from 10 to 16 plications. The 

 hinge width always equals or exceeds the width below, but the speci- 

 mens in the collection are not auriculate. 



'Hall mentions this in Vol. I\^ Pal. N. Y., p. 867, p. 269. He says : "The 

 specimens of the Hamilton group of New York are usually small, measuring about 

 half an inch in length and breadth ; the largest one seen by me being a little more 

 than eleven-sixteenths of an inch in width and about eleven-si.xteenths in length from 

 the apex to front of valve. In some Canadian specimens the length and width 

 are about seven-eighths of an inch." 



