204 
BULLETIN OF THE BUEEAU OF FISHEEIES 
and as Alaskan shells, on the whole, are older than those from the Columbia River 
district, it seems probable that " var. nuttalUi^\v^a,s, described from younger shells 
than were used by Dixon for the original description. The direction of the rib 
varies between shells, but so far as can be determined there is no variation that 
is peculiar to or confined to one bed. 
In the growth of the clam both length and width increase, but not in con- 
stant ratio. There is a variation between individuals of the same age and an in- 
crease in average width with age. The average relation of length to width (in 
percentages) at each age is plotted in Figure 1. The variation at each age is ap- 
parent; for example, at 3 years of age the width of eight out of every ten shells lay 
between 37.5 and 42 per cent of the length. If sufficient records are used to give 
a reliable average, it is seen that with increasing age the average width rises from 
about 38 to 43 per cent of the length. This change of relative width appears to be 
more closely correlated with age than with size. In comparing specimens of the 
same age from various localities we have been imable to find constant differences 
of significant size as compared with individual variation. 
From what has been said it is clear that, in the description quoted above, the 
influences of age and relative size have not been considered, and that clams from 
the ranges of these two varieties do not differ significantly in the characters of di- 
rection of rib or of width of shell nor, so far as can be determined, in other fea- 
tures apart from those directly dependent upon environment. It will be noticed 
that " var. alia " is not included in this discussion. It is unsuited to canning and 
therefore is not considered in this paper. A thorough study of the shell and the 
soft parts shows it to be a separate species, distinct from S. patula. 
The writers feel, after visiting beds on all parts of the coast and examining 
many thousands of shells, that the above views are sound. Excluding valid species, 
such as " var. cdta " and S. hicida^ which do not form a part of the commercial 
catch, we are dealing with a single form. Therefore, comparisons of its reaction 
to features of environment on different parts of the coast are valid. A more de- 
tailed consideration of these and other points of biological interest will be given 
in a later paper. 
ANATOMY 
Everyone who handles clams has noticed some of the more conspicuous parts 
and, since the mollusk is so different in structure from ourselves and other mam- 
mals, has wondered what the various organs are and how they work. The follow- 
ing brief sketch is intended to answer some of the most common of these questions 
and to give a glimpse of the plan of organization of a type of animal strange 
to most of us. A number of features of the anatomy of the razor clam merit 
more attention than is given here and may be treated later. 
The clam, like other members of one group of mollusks, is protected by two 
similar shells or valves (hence the term Mvalves), which are formed on the right 
and left sides of the animal, the back or dorsal side being that where the valves 
are joined together. This shell, which is so striking a feature of these animals, 
is a product of the mantle, a soft structure also characteristic of this group. 
