6 GLOCHIDIA OF FRESHWATER MUSSELS. 



glochidia. And, again, these short-period breeders, particularly sev- 

 eral of the Quadrulas, may have in the marsupium at the same time 

 embryos in all stages from the earliest on up to those with perfectly 

 developed glochidial shells. As an instance of the more or less con- 

 fused state of our present knowledge of the breeding periods of the 

 different forms, in the tables of "periods of gravidity" to foUow I 

 have placed Quadrula heros among the long-period species, but, I 

 must admit, with considerable hesitation. As pointed out by 

 Lefevre and Curtis (1912),° Frierson found it gravid in Louisiana in 

 October (embryos), again in November, and immature glochidia in 

 January, while their own observations record the occurrence of early 

 embryos in May. The late J. F. Boepple found it gravid (immature 

 glochidia) in the Ohio River in October and November. 



Lefevre and Curtis give Plagiola elegans as one of the long-period 

 breeders, and probably this is correct, but the only times at which 

 we have found them gravid at Fairport, or elsewhere, are during May 

 and July. Both early embryos and glocliidia have been found in 

 P. donaciformis during July, but at no other time, so that with our 

 meager knowledge of these forms it seems rather risky to include 

 them among the long-period breeders at the present time. 



In the following tables of gravidity it should be borne in mind that 

 records are for months during which it is known the species bear 

 glochidia of sufficient development to begin their parasitic life, except 

 in the case of Quadrula Jieros and Cyprogenia irrorata, as previously 

 shown. 



a Op. cit.. Bulletin of the Bureau of Fisheries, vol. xxx, p. 144. 



