184 MOLLUSCA. 
ments. The shell is placed on the back with the spiral part 
behind, and the row of holes on the left side, through which 
some of the filaments are protruded. The animal is attached 
to the shell by a single large muscle. The entry to the 
branchial cavity, which likewise contains the termination of 
the rectum and oviduct, is on the back. The gills are in two 
ridges, consisting of complicated branched filaments. At 
the entrance of the cavity, the cloak is furnished with a slit, 
the left margin of which rests upon the pillar of the shell. 
The edges of this slit are furnished with filaments, which 
pass through the anterior holes of the shell. The use of 
this singular arrangement is unknown. The branchial ca- 
vity likewise contains the viscous organ, in common with 
the Pectinibranchie. 
The hood is emarginate, with a long tentaculum on each 
side, behind which, towards the side, is a cylindrical protu- 
berance, bearing the eye at the top. The mouth is in the 
form of a short proboscis, with two corneous plates as cheeks, 
and a long narrow tongue extending backwards, and co- 
vered with spines. The pharynx is dilatable, with internal 
folds. The salivary glands are very small. The gullet is 
very short. The stomach is divided into two portions, the 
first of which is striated longitudinally with a glandular struc- 
ture, and receives a biliary duct. The second is separated 
from the former by a valve, is smaller, with transverse striee, 
and a double ridge. It likewise receives bile through two 
apertures. There is another valve at the pylorus; and the 
intestine, after making some turns, is surrounded by the 
heart. There is an auricle on each side, receiving the aér- 
ated blood from each of the gills. 
2d Tribe. 
Shell conical, simple, or slightly revolute at the apex. 
