184 MOI/LUSCA. 



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 Pectinibranchiae. 



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 

 fdrmof 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 striae, 

 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 aer- 

 ated blood from each of the gills. 



2d Tribe. 



Shell conical, simple, or slightly revolute at the apex. 



