614 
BULLETIN OF THE BUREAU OF FISHERIES 
The annual growth or first-year line has been assumed, in this discussion as 
elsewhere, to mark an interruption in growth. Indeed, indication of autumnal growth 
interruption among adults has been found. However, and especially in the upper 
valve, the line in question is not marked by a noticeable ridge or “ terrace ” but by color 
difference. In the lower valve the growth outside the line is unpigmented and, until 
discolored by growths and stains, pearly white, and is much more noticeable in this 
valve than in the upper. In time, however, the older part of this white growth often 
becomes so discolored as to make difficult the determination of the line. No such 
difficulty is encountered with the upper valve. In it the white (or light) growth is 
not long continued (ordinarily for a width of about 1 millimeter) and is followed by 
the usual darkly marked shell material. Obscured by extraneous growths and dirt 
and even darkened somewhat by stains, with a cleaned shell it stands out plainly 
against the dark of the upper valve and, except very rarely, is unmistakable. 
ENVIRONMENTAL FACTORS 
BOTTOM 
Of the vast array of factors affecting a salt-water animal and constituting its 
environment, only temperature, salinity, current, depth, and bottom are directly 
considered here. The term “bottom” is used to include not only the soil but also 
its vegetation. As previously noted, the bay scallop is almost confined to grassy 
(chiefly Zostera) areas. Just why this is the case seems not to have been explained. 
The writer suggests that it is because early postveliger stages generally find satisfac- 
tory conditions for survival only where the vegetation affords suitable conditions for 
attachment above the substratum, and because subsequent migration is so slight as 
to leave nearly all scallops in grassy areas. 
Grassy bottom, therefore, may be taken to be generally necessary for the bay 
scallop’s existence in certain early stages of development. What its influence is on 
the subsequent life of the scallop, the writer is not prepared to state. Belding (1910) 
believed that much vegetation retarded growth. Although some of the best growing 
areas are very grassy, it is possible that growth in these areas would be better if the 
vegetation were less dense. However, it seems that locally the density of the vege- 
tation is not very important in the growth of the scallop. This is a point of impor- 
tance if scallop culture were to be developed. Possibly nongrassy areas would give 
better growth and prove more satisfactory for planting than grassy ones. On the 
other hand, scallops, which normally shift little, might dislike bare bottom and scatter 
badly. The type of soil influences the appearance but, within suitable limits, has 
little other direct effect. 
DEPTH OF WATER 
The depth of water is important to scallops in so far as it protects them from 
the effects of severe cold or from their enemies. The herring gull catches scallops 
only on flats exposed or nearly exposed at low water. The depth affords some pro- 
tection from man in two quite opposite ways. In areas where raking is the only 
legal method of taking scallops, the depth of water over scallops sometimes is suffi- 
cient to be of protection from rakers. In other areas, where scallops are small and of 
such little value that raking them seldom is considered profitable, there is sometimes 
so little depth of water that even the small dredge boats can not navigate. This, 
of course, serves to protect the scallops from man. Sometimes in severely cold 
weather, as that which occurred late in December, 1925, there is considerable mor- 
