142 



BULLETIN OF THE BUREAU OF FISHERIES. 



Table i6. — Some Noncommercial Mussels, with Indication of Months During Which Females 



Have Been Found with Glochidia. 



It will be observed that, generally speaking, the several species of Quadrula and 

 Unio, as well as Pleurobema asopus (bullhead), Tritogonia tuherculata (buckhom), and 

 Ohliquaria reflexa (three-homed warty-back) are short-term breeders, while the species 

 of Lampsilis, as well as Obovaria ellipsis (hickory-nut), and Symphynota complanata 

 (white heel-splitter), Plagiola securis (butterfly), and others are long-term breeders. 

 Most interesting is the case of the washboard, Quadrula heros, which, from its taxonomic 

 position, would be expected to have the short summer breeding season, but which at 

 least simulates the long-term breeders. The glochidia become mature from early 

 autumn to winter, apparently varying with the latitude, but so far as known are not 

 held for a long period after maturity. They react like the short-term summer breeders 

 when removed from the water in that they quickly abort the contained glochidia. It 

 may be either that its relationship has been incorrectly appraised or that it represents a 

 transition stage from the short-term to the long-term breeding class. Certainly it is 

 the one species of mussel subjected to close study which has never been found to have 

 either eggs or glochidia in its gills during the summer months. 



Finally, it may be remarked that the terms "short-term" and "long-term," as 

 applied to the breeding season, are perhaps inappropriate and misleading. So far as 

 we know, in all species (except the washboard, in one respect) the development of the 

 egg into the glochidium follows promptly on ovulation, occupies a period of a very few 

 weeks, and occurs during warm weather. The short-term breeders are those which 

 throw out the glochidia at once, while the long-term breeders carry them over until the 

 following year. It seems to be a general rule that the short-term breeders pass through 

 all phases of reproductive activity on a rising temperature, while the long-term breeders 



