10 



THE NAUTILUS. 



Observations upon the seasons of breeding reveal further pecu- 

 liarities. Among lots examined in May and November were 

 found individuals carrying in the marsupial gills embryos rep- 

 resenting all stages of development except unsegmented eggs. 

 The following counts from two collections will illustrate this : 



Locality. 



Moline, 111.. 

 Fairport, la. 



Date. 



November 7, 1913. 

 May 1 , 1914 



Stage of Gravidity. 









This lack of uniformity in the late fall and early spring 

 counts, it will be seen, does not correspond with the usual con- 

 ditions to be found in the bradytictic or winter breeders. 



In the absence of parasitism this species must lose the usual 

 method of distribution through the migrations of the host fish. 

 What seems to be a compensatory provision for this loss is to 

 be seen in the peculiar light and flattened type of shell of the 

 juvenile, which subjects it to ready transference by water cur- 

 rents. I have described in another paper * with fuller discus- 

 sion the finding of this species in artificial ponds and reservoirs, 

 whither, in the loss of the parasitic habit, they had been carried 

 doubtless by the water supply. 



To summarize: 



1. Quadrula heros as compared with other Quadrulas and 

 members of the Crenodonta group shows a postponement of 

 breeding time from summer to autumn and winter. 



2. Margaritana monodonta possesses exceptionally small glo- 

 chidia, and there is evidence of at least two broods in a season. 



'Howard, A. D. , 1914. A Second Case of Metamorphosis without Para- 

 sitism in the Unionidse. Science N. S., vol. xi, no. 1027, pp. 353-355, Sept- 

 4, 1914. 



