OCCURRENCE IN VIRGINIA OF GREEN-GILLED OYSTERS. I4I 



Other observations on, specific gravity and temperature were recorded as follows : 



At the same time with these observations, examinations were made of the contents 

 of the stomachs of several oysters just taken from Croonenbergh's Bar, and in every 

 case diatoms or the frustules of diatoms were found that were of exact description of 

 the Navicula ostrearia. 



In a similar manner, as at Lynnhaven, the water of Back River was studied. Where- 

 ever a water sample was taken, oysters were dredged and in every case showed the 

 greengill. The weather there was the same as had been experienced at Lynnhaven, 

 and the water was very much roiled. The specific gravity and temperature of the 

 water varied from 1.015 to 1.017 and from 8.5 to 10° C, respectively. In the five 

 samples taken, approximately half a mile apart, two contained diatoms which were 

 identified as Navicula ostrearia. The observations in Back River were as follows: 



The Navicula ostrearia was also found in the green scum that clung to the shell of 

 one of the oysters dredged in this observation. 



On January 19, 1916, a sample of water from the western arm of Lynnhaven Bay, 

 Va., was examined after a two days' shipment during very cold weather. The sample, 

 despite the cold weather, yielded many different kinds of vegetable organisms, among 

 which was obser\'ed the Navicula ostrearia. On February 18, 1916, a water sample 

 from Lynnhaven Bay was examined that showed by far a larger number of organisms 

 with the characteristic Navicula ostrearia appearance than any water sample yet taken. 

 On March 17 another water sample was received from Lynnhaven and examined, but 

 this showed no Navicula organisms whatsoever. Possibly this absence of the above- 

 mentioned organisms was due to the fact that the sample was taken in deeper water 

 and with a large bottle that had a very narrow neck. The shape of the bottle was in 

 itself enough to prevent obtaining an average and acceptable sample. On April 17, 

 1 91 6, another water sample from Lynnhaven arrived and was examined. This, how- 

 ever, showed no Navicula, but the absence on this occasion of the diatoms could be 

 reasonably laid to the report that the greengills were clearing up in the bay and that 

 no very green oysters could be found. Those which did have any pigment were very 

 pale. On June 14, 1916, a similar water sample was examined, but this showed no 

 Navicula ostrearia. 



In an effort to ascertain whether the Navicula ostrearia inhabited the waters where 

 the greengill had never been known to exist, and to further the theory that the blue 

 69571°— 18^— 10 



