42 BIOLOGICAL SURVEY OF 



This brings up the question of rarity. We hear constantly 

 that certain creatures are rare. Is this so or does it just mean 

 that they happen to be scarce in some particular place or that 

 they are not easily found! They certainly must be in abun- 

 dance somewhere or the continuance of the species would not 

 go on. The truth probably is that the dredge that has been 

 scraping the bottom has missed one of the centers of popu- 

 lation. 



Take as an example the mollusk Panomya arctica, which 

 gets down into crevices in the rocks. We were given one 

 adult by a fisherman who was dragging for scollops, and in 

 one of our dredgings we took several very young specimens 

 embedded in a lump of hard clay which the dredge tore from 

 the bottom. They undoubtedly occur in abundance, but their 

 habit of getting into crevices prevents the dredge from dis- 

 lodging them. Some of the Ascidians which attach themselves 

 to ledges must be far more numerous than the dredgings 

 would indicate. 



Then again, we have the questions of seasonal distribution, 

 of temperature and depth, and the combination of the two. 

 Some years the waters will be filled with the Medusa Aurelia 

 flavidida, while in others there will be only a moderate 

 amount. This, however, I have noticed to be connected mth 

 the movement of anchor ice on the shores which had destroyed 

 the sessile winter forms. Some years we have large numbers 

 of Cyanae arctica floating in the Bay and at times these have 

 become quite large. One year, dozens of individuals were cast 

 up on the shore of Frenchmans Bay averaging close on to 

 3 feet in diameter, while the average size is less than one-third 

 of that. At times when the conditions are ripe, the Bay mil 

 be full of Ctenophores, while we see very few at other times. 



This was most strikingly demonstrated in Augnist, 1931, in 

 the inner Bay. Early in the month we noticed a slight red 

 coloration in the Bay between Stave and Jordan Islands. The 

 summer weather was abnormal with temperature far above 

 the average for the month and a complete lack of intervening 

 cool days, with less wind than had been on the Bay for 10 



