142 BULLETIN OF THE BUREAU OF FISHERIES. 



all essential points agree closely with ours. He includes among "winter breeders" 

 several genera which we have not had under observation, namely, Truitcilla, Micromya, 

 Ptychobranchus , and Anodontoides , while Arcidens, which we have recorded, does not 

 appear in his list. 



There is given below a brief summary of our breeding records for the genera here 

 concerned. Although in many species we have examined hundreds of individuals and 

 have had them under observ^ation continuously throughout the year, in others the 

 material has been more or less meager and observ'ations scattered, but in most of the 

 forms the records have been adequate for a determination of the general limits of the 

 breeding season. 



Alasmidonta. — Embryos from latter part of July to middle of August. No fully 

 formed glochidia have been seen, as gravid females have not been secured after August. 

 Anodonia. — Embryos from the middle of August to September; ripe glochidia from 

 early October to first of July. A distinct interim exists between close of one period 

 and beginning of next. According to Harms (1909), in European species of Anodonia 

 the eggs are fertilized about the middle of August, all of the individuals entering upon 

 the breeding season at nearly the same time, and by the middle of October almost all 

 of the females are gravid with glochidia. 



Arcidens. — Glochidia in winter months. Only a few individuals secured. 

 Cyprogenm. — Glochidia in November. 

 Dromus. — Glochidia in November. 



Lampsiiis. — Embryos from first of August to late September; glochidia from late 

 September to first of August. Our most complete record concerns this genus, several 

 species of which {anodontoides, ligamentina, recta, suhrostrata, ventricosa) we have 

 repeatedly had under observation continuously throughout the year. The gravid 

 period seems to be more extended in Lampsiiis than in any other genus, for, although 

 June is apparently the month when the liberation of glochidia is at its height, some 

 females bearing glochidia may still be found, but in diminishing numbers of course, until 

 the beginning of August, a time when the next season is just setting in. Since ripe 

 glochidia may be obtained in abundance from October to July, inclusive, and since 

 Lampsiiis furnishes several species of commercial value, the extended period of gravidity 

 in this genus becomes of the greatest importance in artificial propagation, as material 

 is available for the infection of fish throughout the greater part of the year. 



Ofcowna.— Glochidia during the fall, winter, and spring months. Spawning must 

 occur before June, as no glochidia have been encountered in June, July, and August, 

 although a number of females have been obtained during these months. 



Plagiola. — Ripe glochidia during the winter and as late as the end of July; no 

 embryos have been obtained. 



Strophitus.— Embryos from late July to middle of August; glochidia from November 

 to middle of July. The interval between the seasons is very short, much shorter than 

 that observed by Ortmann (1909), who records an interim from May 22 to July 11. 



