202 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Enemies .— One important fact which must be considered in developing any method 
of clam-culture is that the clam in its attached condition, and when exposed on the 
surface of a bed, is destroyed in vast numbers in many localities by one or two natural 
enemies. The worst of these is that curse of the oyster-culturist in northern waters — 
the star-fisli. Many extremely interesting and important observations in regard to 
this creature’s habits of destroying clams and other forms have been made during the 
past summer by Dr. A. D. Mead. These observations show that the star-fish, even 
when minute in size, is terribly destructive to the young clams. 
Another enemy of the young clam is the oyster-drill ( Urosalpinx). Many clam 
shells have been taken from the surface sand of the bottoms which exhibited the clean 
perforation filed by this creature. Shells so pierced were from 3 mm. to 2 cm. or more 
in length. As I have never found drilled shells in any great numbers in one locality, 
it would appear that the clam is not seriously menaced by this foe. The adult clam, 
deep below the surface, is probably not disturbed by other enemies than man. 
SUMMARY. 
To recapitulate the principal points established in the foregoing description of the 
life-history of the clam, beginning after the swimming larval condition, we notice that 
the breeding season in Narragansett and Buzzards bays probably extends through 
May and June into July. Beginning my observations late in June, I have not been 
able to determine its limits with any certainty. After the free-swimming larval 
period, the young clams attach themselves by means of a byssus, which is produced 
from a byssus gland in the foot. Attachment is made to various bodies in the water. 
Glams may be found so attached from the latter part of June to the 1st of August. 
They are to be found in certain localities in immense numbers. The attached indr 
viduals measured varied in length from 0.4 to 7 mm. The shape of the smaller 
individuals differs greatly from that of the adult in being much more rounded, with 
umbones widely separated laterally. As they become older, they gradually assume 
the outline which characterizes the adult, but in so doing the umbones come to be 
situated relatively far forward, and then again move back toward the middle of the 
shell on the dorsal side. This shifting in the relative position of the umbo is due to a 
more rapid growth of the posterior, and subsequently of the anterior ends of the shell- 
In the smallest forms examined, the mantle folds were in concrescence ventrally' 
The foot is relatively greatly developed, extending over the entire ventral side of the 
visceral mass. The siphons have the general characters of those in the adult, but are 
filmy and may be retracted within the shell with very great quickness. 
Clams of all sizes apparently free themselves from their attachment. The byssus 
is cast off and the creature climbs from one point to another by means of the foot, 
sometimes reattaching, sometimes falling free to the bottom. In the sand, unless 
it be excessively fine, individuals less than 2 mm. in length are rarely able to cover 
themselves, though they always make the attempt. Those 5 or 6 mm. long are appar- 
ently able to burrow beneath the surface of any clam shore. 
Having attained a lodgment in the sand, all clams observed proceed immediately 
to form a byssus thread, which is attached to sand grains and pebbles. This tends to 
secure the creature, so that, even if water currents or the action of the waves should 
dislodge it from its burrow, it would not be carried so far from its original position as 
would otherwise occur. Of their own accord, these clams frequently leave the first 
burrow, wander about, and form another, some individuals repeating the process many 
times. A time finally comes when they dig into the sand to remain permanently. 
