144 PROCEEDINGS OF THE MALACOLOGICAX SOCIETY. 



is then retracted and the process repeated. In tliis manner the 

 animal progresses slowly by a series of loop-like movements of ex- 

 tension and contraction, in which the sharp -pointed and freely- 

 projecting operculum plays a very important part, I am inclined 

 to believe that progression in Pterocera is effected in a similar manner 

 rather than by a leaping movement. 



The mantle shows but slight indications of those characteristic 

 processes which secrete the chiAv-like prolongations of the peristome, 

 both these and the anterior siphon being evidently highly retractile. 



On opening the mantle cavity the large grooved penis is seen 

 doubled up within this chamber, the free end being flattened and 

 expanded.' The rectum forms a prominent ridge down the right side 

 of the dorsal wall of the mantle chamber, and the anus is situated on 

 the tip of a pointed freely projecting promontory close to the edge of 

 the mantle. High up, near the upper part of the rectum, and close 

 to the angle between the body and the mantle fold, is the swollen 

 glandular termination of the vas deferens, opening by a small aperture, 

 from which there extends a long open groove (possibly ciliated) down 

 the mantle and body wall to the penis, along the entire length of 

 which it runs. 



The renal aperture, which, like the kidney itself, is large, is placed 

 close to the posterior end of the gill and to the pericardium. Quoy and 

 Gaimard,^ and Kieferstein^ botli speak of the kidney as the uterus. 

 The mucous gland is apparently subdivided into two portions, a large 

 one near the rectum and a smaller one close to the gill. The gill is 

 large and its efferent branchial vein runs along its left border. 



The osphradium (parabranchia, nebenkieme,^ petite branchie') is 

 present as a long granular line situated to the left of the gill and 

 running down to the siplion ; when examined under a lens it is seen 

 to have the structure of a double comb. 



The anterior portion of the body, which tapers off into the foot, 

 forms the convex floor of the mantle cavity, and is compressed dorso- 

 ventrally. It consists almost entirely of a muscle-mass, which is 

 attached to the shell dorsally by the columella muscle, the viscera 

 occupying but a narrow tube in the middle of this mass. 



The mouth opens on the end of the non-retractile muzzle, and is anned 

 with a pair of laterally-placed gelatino-chitinous jaws : it communi- 

 cates with a small buccal mass containing a well-developed odontophore 

 and radula sac ; from this proceeds a short and narrow oesophagus, on 

 which is placed a pair of slightly branched salivary glands opening 

 into the buccal mass. These structures all lie within the muzzle. 

 The oesophagus on entering the body becomes suddenly enlarged to 

 form the crop ; this structure, which is about 4^ inches long, tapers 



* Cams, Icones Zootoniicre, copies the figure of Quoy and Gaimard's female 

 specimen, wliicli lie calls a male and letters the foot as the ])euis. 



^ Voyage de I'Astrolabe. Zoologie par MM. Quoy and Gaimard, torn. iii. p. 878, 

 pi. xlix. fig. 18; '' Sfromb/m lamhis.'''' 



3 IJronn's Klassen u. Orduung. d. Thier-lleichs. Bd. iii. Abth. 2. Malacozoa, 

 18G2-GG. J'l. Ixxxiii. lig. 2, u. 



