size 1 as follows: 200, 2,520, 6,800, 3,780, and 2,960. The average number 

 per sample is 3,252. This is plotted on figure h as a bar covering the same 

 3 days. 



Because of the scale necessary to accommodate high abundances, no count 

 below 11 per 35 gallons is recorded on the graphs, but reference is made in 

 the text to the occurrence of these larvae. 



Surface temperatures were taken regularly in Wickford Harbor, Since 

 the mean depth at low water is only 2 to 3 feet, no other levels were 

 measured. Both surface and bottom temperatures were taken in Greenwich 

 Bay. Since it is logical to assume that whatever influence water tempera- 

 ture has on spawning will be of the water immediately over the bottom, only 

 the bottom temperatures in Greenwich Bay are presented in this report. 



IDENTIFICATION OF THE LARVAE 



Mya larvae 



The literature contains photomicrographs and descriptions of Mya 

 larvae of sufficient accuracy to make identification relatively simple. 

 Sullivan's (1 Q 1±8) description was particularly instructive and I readily 

 found and accepted as diagnostic the brown pigment which begins under the 

 shoulders at 120 microns and, as the larva grows, proceeds in a broken ring 

 around the animal and into the visceral mass, Thorson (19U6) also mentions 

 this pigment in specimens nearly 200 microns long and states that it will 

 "no doubt prove to be a reliable specific character „" This pigment ring, 

 Together with the larva's lack of color otherwise,, and with its transparency 

 and shape, make the Mya larva one of the easiest of all bivalve larvae to 

 identify. The identify of Mya larvae was further substantiated by holding 

 late umbone stage specimens in beakers where with suitable care they readily 

 grew to a size and shape characteristic of Mya juveniles approximately 1 mm. 

 long. 



Venus larvae 



Identification of Venus larvae is somewhat more difficult. No ade- 

 quate description such as that for Mya exists in the literature, Loosanoff 

 and Davis (1950) include photomicrographs of Venus larvae, and they provided 

 mounted stained specimens and preserved series of artificially reared larvae 

 to aid in identification. 



Venus larvae are identified by a combination of features; (1) Shape, 

 which tends to roundness after the straight-hinge stage is past) (2) size, 

 which ranges from approximately 110 microns as early straight-hinge larvae 

 to approximately 225 microns when they disappear from the plankton; (3) 

 color, which is bright yellow, usually more pronounced toward the perimeter 



