112 THE NAUTILUS. 



found gravid by me (of this group) was a Q. trapezoides, May 10, 

 1901. Since that time I have opened and examined dozens of gravid 

 specimens. They are gravid from May to September, after which I 

 have never found eggs in their gills. Of Quadrula perplicatus Con- 

 rad, 1 have taken but two specimens, June 7, 1901, and August 19, 

 1903. In one the gills (all four) were but one-half filled with eggs, 

 the lower half of each gill being empty. The other was a normal 

 Qaadrula. Quadrula heros had never been taken gravid by me 

 until October 8, 1903, a young specimen proved to be in that condi- 

 tion. Its gills (four) were packed full of uncountable ova. These, 

 under the microscope, were perfectly spherical and undeveloped, 

 showing that they were recently extruded from the ovary. 



On November 24, 1903, a batch of about fifty were brought me by 

 a negro, to -be sent to Mr. Chas. Conner, of Philadelphia. After 

 packing fifteen or twenty for him, the remainder were opened, and to 

 my surprise, fully half were gravid. Mr. Conner reported several of 

 his also gravid. Most of these eggs were not yet developed into 

 glochidia, several specimens having eggs in the " mulberry stage." 



January 7, 1904, out of seven specimens opened, four proved to 

 be gravid. These were full of glochidia, but they did not seem to 

 be perfectly developed or ready to be extruded, being very sluggish. 



These observations prove two points : First, that the plicata group 

 belongs safely to Quadrula, as defined by Mr. Simpson, and that the 

 specimen noted by Sterki and H. von Ihering must have been ab- 

 normal. Secondly, that the seasons of ovulation are different in 

 different species of the same group, Q. trapezoides being a summer 

 breeder, while Q. Jieros is an autumn or winter breeder. 



THE MOLLUSKS OF CEDAR LAKE, INDIANA. 



BY FRANK COLLINS BAKER. 



Some months ago, the Monon Railroad invited the writer to visit 

 Cedar Lake, Indiana, to witness the seining of the lake for " pirate" 

 fish, such as carp, gars and pickerel. Incidentally a collection of the 

 mollusks was made, which seems of more than passing interest. The 

 lake is a body of cold water, of considerable extent and of great depth 

 in places. The species collected are as follows : 



