OF MOLLUSCA. 159 



into the shell ; frontal lobes triangular, fringed on the edge. Foot 

 round, enclosed ; lateral membrane very wide, fringed on the edge. 

 Operculum horny, thin, circular, many-whorled. 



1. S. maculata, t. 109. f. 1, 3. 



2. S. sulcifera, Adams, Gen. Moll. t. 49. f. 8 b, c, operculum. 



b. Operculum none. Animal larger than shell, produced behind. 



2. Stomatia. 



Shell subspiral, oblong ; whorls keeled or tubercular, plicate near 

 the sutures ; spire prominent ; aperture wider than long, pearly 

 within ; frontal lobes digitated ; foot very large, tubercular, pro- 

 duced behind ; lateral membrane fringed, with a fringed crest under 

 the eyes on the left, and a slight projecting fold on the right side, 

 leading to the respiratory cavity. Operculum none. 



1. S. rubra, Adams, Gen. Moll. 436. t. 49. f. 9. 



The animal of Stomatia and Gena has, like Harpa, the habit 

 of throwing off the hinder part of the foot when frightened, or placed 

 alive in spirits. 



3. Microtis. 



Shell suborbicular, spiral, depressed, with two tuberculated ridges ; 

 spire slightly prominent ; aperture very large, wider than long, 

 pearly within ; pillar-edge spiral, visible to apex of spire. Living on 

 sand within tide line. Animal like Stomatia, but with a deep ante- 

 rior fissure for the head, and the front edge bilobed. Operculum 

 none. 



1. M. tuberculata, Adams, P. Z. S. 1850, 36. t. 8. f. 8-12; Gen. 

 Moll. t. 50. f. 1. 



4. Gena. 



Shell oblong, elongate, ear-shaped, subspiral ; spire flattened, 

 nearly obsolete ; aperture large, oblong. Animal oval, depressed ; 

 frontal lobes plumose. Foot very large, tubercular, produced behind. 

 Lateral membrane not fringed, more or less extended, and partially 

 covering the shell. Operculum none. 



1. G. lutea, t. 109. f. 5. 



2. G. nigra, t. 109. f. 4. 



The foot elongated behind, the shell granulated above ; when the 

 animal is put in spirits, the hinder part of the foot suddenly con- 

 tracts into a subglobular form, and separates by a transverse section 

 from the rest of the foot. 



Lingual membrane of Gena elegans linear elongate, rather dilated 

 in front, transparent. Teeth 00 * 5 • 1 * 5 • 00, placed in a rather 

 arched series ; central tooth narrow, elongate, contracted, and very 

 narrow in the upper part ; apex small, triangular, reflexed, denticu- 

 lated on the edge ; inner lateral teeth 5 • 5, linear elongate, placed 



