144 BULLETIN OF THE BUREAU OP FISHERIES. 



the latter part of May to July 9; glochidia from June 20 to August 8. This is a typical 

 record for a summer breeder, and there can be little doubt that the species must be placed 

 in this group. On the other hand, Sterki (1898, 1903) states that all forms which have a 

 differentiated marsupium carry their glochidia over the winter, and Ortmann (191 1) 

 includes Ohliquaria in his LampsiliiujE, all of which he says are "bradytictic," although 

 specific reference to the breeding season of this genus is not made. Since, however, 

 we have not had an opportunity of observing the species during the fall and winter, 

 it is possible that it has the long period, although, if such is the case, its season begins 

 two months earlier than that of any other species in this class — a quite improbable 

 supposition. For the present, at all events, we must consider it a summer breeder. 



Plcurobema. — Embryos from early June to early August ; glochidia during July. 



Quadrula. — Embryos from late May to middle of August ; glochidia from early June 

 to middle of August. Hundreds of females belonging to different species of this genus 

 have been examined throughout the rest of the year, but gravid individuals have never 

 been encountered except during the months indicated. 



It should be mentioned that in the case of 0. heros Frierson (1904) has not found 

 this species gravid in Louisiana until October, when embryos were found. Young 

 embryos were again encountered in November and immature glochidia in January. He 

 concludes that hcros is an exception in the genus and is not a summer breeder. Our 

 observations on this species are very meager, but since we have found it bearing young 

 embryos in the latter part of May, they would seem not to be in accord with those o£ 

 Frierson. 



According to Harms (1909), Margaritana, which breeds in Europe in July and 

 August, produces two successive broods during that time, from sixteen days to four 

 weeks, according to temperature, being required for the development of each. Although 

 we have not determined it beyond all doubt, our records strongly indicate that the species 

 of Quadrula also spawn twice during the season, first in June and July and again in July 

 and August. This, however, could not be definitely proven without a most extended 

 series of observations, and possibly not unless individual females were kept in aquaria 

 under close observation throughout the breeding season. 



Unio. — Embryos from early June to early August ; glochidia from middle of June 

 to middle of August. Conner (1907) records U . complanatus as beginning its breeding 

 season in April, and Lea (1S63) found it gravid in Ma}'; but we have not had an oppor- 

 tunity of examining any species of the genus during these months. According to Harms 

 (1909) the breeding season of Un-io in Europe begins early in March, or, if the weather 

 is cold, not until the end of May. 



