TROi'iDoi.F.prus P\'\UNA AT Canandaioua Lakk, X. Y. 149 



PART II. A STUDY OF A IIAIMILTON FAUNULE FROM 

 CANANDAIGUA LAKE, N. Y. 



Ini'roduction. 



The material on which the preceding studies were based, was, as is 

 stated in the introduction to ])art I, obtained from a clayey limestone 

 by etching with hydrochloric acid. I'he outcrop from which the 

 blocks were taken is in a ravine on the west side of Canandaigua 

 Lake, New York, where the silicified fossils occur in several layers, 

 but all within the seventy-five feet al)ove the " Encrinal " limestone of 

 that region. 



Sixty-five pounds of the limestone, when treated with acid, yielded 

 about 15,000 shells which were sufficiently perfect to be saved for 

 making up collections, and there was fully as much fragmentary 

 material. In most cases the two valves of the shells are separated, 

 but even taking that fact into consideration, the material must repre- 

 sent the remains of at least 10,000 individuals. From the vast number 

 of the shells, it is evident that they could not have lived contempor- 

 aneously in the small space which contains their remains, but the rock 

 must represent the accumulated shells of many years. 



As the method used in obtaining the material from the matrix 

 eliminates all the collector's personal equation, all the minute speci- 

 mens are detected, and all individuals of each species saved. Thus 

 the collection gives a very accurate idea of the fauna existing in the 

 region at the time the rock was being deposited. It cannot, however, 

 be taken as absolutely accurate, as there probably existed species 

 which were not preserved and it is also possible that a larger quantity 

 of the rock might have afforded a greater variety of forms. 



The object of this part of the paper is to study this faunule in com- 

 parison with the other faunas of the New York-Ontario province, and 

 to give an annotated faunal list. 



Conditions of Sedimentation. 



The rock is fine grained and contains much very fine clay. In 

 some cases this clay is evenly distributed throughout the layer and is 

 cemented by the lime. In that case the action of the acid is free and 

 as a result the fossils are easily separated from the residue of fine clay 

 by washing. Other layers have an inch or more of almost pure clay 



