263 
There is still another method of locomotion to be described. 
Solenomya is able to swim quite actively. It always swims with the 
anterior end of the shell pointed forward!) and the movement consists 
of a series of short darts that remind one of the swimming of a 
squid. Each dart is accompanied by certain movements of the foot 
that are very misleading when considered by themselves. 
Not infrequently ?) it has been supposed that the swimming is 
accomplished by the energetic spreading of the muscular flaps accom- 
panied by the retraction of the foot. That the animal is able to 
burrow its way through water much as it burrows through mud. 
Others have found that a strong stream of water is thrown from 
the mantle chamber through the small posterior opening at intervals 
corresponding to 
each forward dart, 
but the method of 
expelling the water 
seems never to have 
been understood. 
It will be ne- 
cessary to describe 
the structure of cer- 
tain parts in order to 
make the mechanics 
of swimming clear. 
The shell is 
rather delicate and 
nearly cylindrical. 
The cuticle of the 
Fig. 8. 
Fig. 7. Solenomya velum, seen from the right side, with the foot protruded, 
f foot; ms margin of the calcareous portion of the shell, seen through the rather trans- 
parent cuticle; po posterior opening of the mantle chamber. In position this opening 
corresponds to the siphons, but it is a single opening. 
Notice the alternately thick and thin portions of the cuticle, radiating from the 
beaks to the free border, 
The thickened portions insure great elasticity, the thinner portions allow for the 
plaiting that takes place when the cuticle is folded into the mantle chamber, 
Fig. 8. Solenomya velum, seen from the ventral side, with the foot protruded, 
ao anterior opening of the mantle chamber; f foot; ms margin of the calcareous portion 
of the shell, seen through the rather transparent cuticle; po posterior opening of the 
mantle chamber. 
1) The posterior movements of this form have been described under 
the head of leaping movements. 
2) See: The Invertebrate Animals of Vineyard Sound and Adjacent 
Waters, by A. E. Verrixt and 8. I. Smith, p. 66. 
