MOLLUSCA. 203 
several individuals; each having its own heart, respiration, 
and system of nutrition, but fixed on apeduncle that branches 
from a common creeping stem, and all being connected by 
a circulation that extends throughout. Their parts of such 
transparency that their interior is easily seen. Their ex- 
ternal shape is that of a pouch, compressed at the sides, and 
fixed at the hind part of its base upon the peduncle. 
Its two openings are in the form of very short tubes; that 
of the mouth at the top of the pouch, and that of the funnel 
in front. The longest diameter, from the peduncle to the 
space between the openings, is about ‘085 inch. 
The outer covering is a tough coat, a continuation of the 
peduncle, more pliable near the openings; lined interiorly 
with a soft substance or mantle, in which a ramifying circu- 
lation is very distinct. A great part of the interior is occu- 
pied by the branchial sac, which is subcylindrical, flattenec 
at the sides, and has its axis vertical ; its cavity terminating 
upwards in the oval opening, and being closed at the bot- 
tom. It is united to the envelope, or to the mantle above 
and behind; the juncture, beginning in front of the oval 
opening, extends backwards on each side of it, and then 
downwards in two lines ; between these, along the middle 
of the back, is a vertical compound stripe, that seemed to 
me cartilaginous. At the bottom the sac appears to be en- 
veloped by the soft substance of the mantle, but at its sides 
and front a vacant space is left between them, that ends in 
the opening of the funnel. The branchial sac is more com- 
pressed towards its lower part ; and here are placed, exter- 
nally to it, the heart on the left, and the stomach and other 
viscera on the right side, the vent opening upwards at the 
front into the funnel. On its sides and front the sac is per- 
forated by four rows of nayrow, vertical, irregularly oval 
