MOLLUSCA : GASTEROPODA. 339 



Helidda (Land-snails), Limacida (Slugs), Oncidiada, Limnceida 

 (Pond-snails), and Auriculida. 



Section II. Operculata. Shell closed by an operculum. In this 

 section are included the families Cydostomida and Adcuiidtz. 



SYNOPSIS OF THE FAMILIES OF THE GASTEROPODA. 

 (AFTER WOODWARD.) 



SECTION A. BRANCHIFERA. Respiration aquatic, by the walls of 

 the mantle-cavity, or by branchiae. 



ORDER I. PROSOBRANCHIATA. The branchiae situated (prosori) 

 in advance of the heart. 



Division a. Siphonostomata. Margin of the shell-aperture 

 notched or produced into a canal. 



Fain. i. Strombidcc. Shell with an expanded lip, deeply notched 

 near the canal. Operculum claw-shaped. Foot narrow, adapted 

 for leaping. 111. Gen. Strombus, Pteroceras. 



Fam. 2. Muricidcz. Shell with a straight anterior canal, the aperture 

 entire posteriorly. Foot broad. 111. Gen. Murex, Triton, Pyrula, 

 Fusus. 



Fam. 3. Buccinidce. Shell notched anteriorly, or with the canal 

 abruptly reflected, producing a kind of varix on the front of the 

 shell. 111. Gen. Buccinum, Nassa, Purpura, Cassis, Harpa, 

 Oliva. 



Fam. 4. Conidce. Shell inversely conical, with a long narrow aper- 

 ture, the outer lip notched at or near the suture. Operculum 

 minute, lamellar. 111. Gen. Conus, Pleurotoma. 



Fam. 5. Volutidcz. Shell turreted or convolute, the aperture notched 

 in front ; the columella obliquely plaited. No operculum. Foot 

 very large ; mantle often reflected over the shell. 111. Gen. Valuta. 

 Mitra, Marginella. 



Fam. 6. Cyprceidt?. Shell convolute, enamelled ; spire concealed, 

 aperture narrow, channelled at each end. Outer lip thin m the 

 young shell, but thickened and inflected in the adult. Foot 

 broad ; mantle forming lobes which meet over the back of the 

 shell. 111. Gen. Cyprcea, Ovulum. 



Division b. Holostomata. Margin of the shell-aperture 

 " entire" rarely notched or produced into a canal. 



Fam. i. Naticidce. Shell globular, of few whorls, with a small spire, 

 outer lip acute, pillar often callous. Foot very large ; mantle- 

 lobes hiding more or less of the shell. Gen. Natica, Sigaretus. 



Fam. 2. Pyramidellidte. Shell turreted, with a small aperture, 

 sometimes with one or more prominent plaits on the columella. 

 Operculum horny, imbricated. 111. Gen. Pyramidella, Chemnitzia. 

 Eulima. 



Fam. 3. CerithiadcB. Shell spiral, turreted ; aperture channelled in 

 front, with a less distinct posterior canal. Lip generally expanded 

 in the adult. Operculum horny and spiral. 111. Gen. Cei ithium, 

 Potamides, Aporrhais. 



Fam. 4. Melaniada. Shell spiral, turreted ; aperture often chan- 

 nelled or notched in front ; outer lip acute. Operculum horny 

 and spiral. 111. Gen. Melanta, Paludomus. 



