88 THE NAUTILUS. 



The scene of most of my observations has been along the Delaware 

 river and Big Timber creek, in the vicinity of Newbold and Wash- 

 ington Park, New Jersey. 



All along the extensive flats there mussels abound, and their empty 

 shells lie scattered along the banks in thousands. 



For the purpose of these observations I have made it a point to 

 patrol that section at low tide some time during every month of the 

 year. 



The work has been attended by many disadvantages, otherwise I 

 should have been able to present a complete record of the matter. 



The varying periods during which the glochidia are extruded by 

 the various species, tends (so it appears to me) to effect their distri- 

 bution ; those spawning when fish are migrating, for instance, would 

 have their distribution extended farther, or more rapidly than other 

 species. Of the species hereabouts, Unio complanatus (Sol.), has 

 given me the best results for the labor expended. My records show 

 that they are gravid but once annually, from April-May to July- 

 August, or, approximately, during four months of the year. 



I have found Lampsilis radiatus (Gmelin), and Unio nasutus 

 (Say) gravid all the year around. Both appear to spawn in June 

 and November, if not also at other times. All the individuals do 

 not spawn at the same time. On June 22, 1907, I found some 

 U- nasutus with the gills half empty, and some still full. 



Anodonta cataracta (Say) is gravid about eight months in the 

 year, the interim occurring during the warm period (May-October). 

 I have found them gravid as late as May 27, and as early as October 

 13. I have found them spawning the latter part of December, to 

 the early part of January* which indicates approximately, as is the 

 case with JJ- complanatus, a gravid period of about four months. 



I have had the good fortune to discover the use of the byssus also. 

 I isolated a gravid specimen in an aquarium, and when the glochidia 

 were extruded, using a magnifying glass, I discovered several of 

 them, with the valve opened wide, hanging suspended by the byssus, 

 from the Anacharis canadensis plants with which the aquarium was 

 stocked. f 



From further observations it appears that they hang thus sus- 



* Nautilus, Vol. XIII, pp. 142. 



f April 19, 1905, Anodonta cataracta, Say. 



