44 
PACIFIC SCIENCE, Vol. IV, January, 1950 
the mid- line to the posterior end as it is tc 
the anterior end. The form of the shell is 
variable as is shown in Figure 3. 
Side views of the shells usually display 
many similarities to those of Cardium. In 
some cases, however, the posterior surface is 
almost completely flat, with the posterior end 
of the shell indicated by a little projection 
and with somewhat of a depression at the 
mid-portion. 
Fig. 2. Lateral view of heart shell. (Slightly 
reduced. ) 
It is frequently observed that a smaller 
shell has a rather elongate shape and a larger 
one has a more rounded shape. This relation 
may also be traced in one shell as is shown 
in Figure 4. When the shell outline is sup- 
posed as cut off at a certain growth line the 
remaining parts of the shell represent the 
form of the younger shell. In this manner, 
a series of shell forms is obtained such as is 
shown in Figure 4 a-i. These figures clearly 
show that the younger form is more elongate 
than the older one. This relationship is shown 
numerically in Table 1. The ratio of breadth 
(lateral width) to height (dorso- ventral) is 
greater in the larger specimens. 
Fig. 3. Outlines of shells of C. cardissa show- 
ing variations in shape of shell, a, b, c, Posterior 
profile; a it b lt c lf d lt lateral profile. 
TABLE 1 
Measurements of the Shell of Corculum cardissa 
LOCALITY 
HEIGHT 
BREADTH 
LENGTH 
THICKNESS 
TOTAL 
WEIGHT 
b/h* 
St 
w / s $ 
cm. 
cm. 
cm. 
mm. 
gm. 
Palao . 
. 6.50 
6.00 
2.50 
0 . 5 - 0.7 
13.4 
0.92 
61.7 
0.217 
Palao . 
. 5.63 
5.20 
2.36 
0 . 5 - 0.6 
8.7 
0.92 
42 
0.207 
Ryukyu . 
. 4.66 
3.87 
2.4 
0.5 
6.5 
0.83 
24 
0.270 
Ryukyu . 
. 3.25 
2.85 
1.45 
0 . 2 - 0.3 
1.99 
0.88 
14 
0.14 
* B/H Ratio of breadth to height, 
t S Surface area in square centimeters. 
tW/S Weight in grams per square centimeter of surface area. 
