266 MANUAL OP ZOOLOGY. 



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. 1. NaticidfS. 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. Pyramidellida. 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. Cerithiada. 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. Cerithium, 

 Potamides, Aporrhais. 



Fam. 4. Melaniadce. Shell spiral, turreted ; aperture often channelled 

 or notched in front ; outer lip acute. Operculum horny and spiral. 

 111. Gen. Melania, Paludomus. 



Fam. 5. Turritellidcs. Shell tubular, or spiral, often turreted ; upper 

 part partitioned off; aperture simple. Operculum horny, many- 

 whorled. Foot very short. Branchial plume single. 111. Gen. 

 Turritella, Vermetus, Scalaria. 



Fam. 6. Littorinidce . Shell spiral, top-shaped, or depressed; aper- 

 ture rounded and entire ; operculum horny and pauci-spiral. 111. 

 Gen. Littorina, Solarium, Eissoa, Phorus. 



Fam. 7. Paludinidce. Shell conical or globular; aperture rounded 

 and entire ; operculum horny or shelly. 111. Gen. Paludina, Am- 

 pullaria, Valvata. 



Fam. 8. Neritidce. Shell thick, globular, with a very small spire ; 

 aperture semi-lunate, its columellar side expanded ; outer lip acute. 

 Operculum shelly, sub-spiral. 111. Gen. Nerita, Pileolus, Neritina. 

 Fam. 9. Turbinidce. Shell turbinated (top-shaped), or pyramidal, 

 nacreous inside. Operculum horny and multi-spiral, or calca- 

 reous and pauci-spiral. 111. Gen. Turbo, Trochus, Delphinula, 

 Euomphalus. 



Fam. 10. Haliotidce. Shell spiral, ear-shaped, or trochoid, aperture 

 large, nacreous. Outer lip notched or perforated. No operculum. 

 Mantle-margin with a posterior fold or siphon, occupying the slit 

 or perforation in the shell. Metapodium rudimentary. 111. Gen. 

 Hcdiotis, Scissurella, Pleurotomaria, Murchisonia, lanthina. 

 Fam. 11. Fissurellid<s. Shell conical, patelliform, with a notch in 

 the anterior margin, or a perforation at its apex, which is occupied 

 by an anal siphon. Muscular impression horse-shoe-shaped, open 

 in front. 111. Gen. Fissurella, Emarginula, Parmophorus. 

 Fam. 12. Calyptrceidce. Shell patelliform, with a more or less spiral 

 apex ; interior simple, or divided by a shelly process to which the 

 adductor muscles are attached. 111. Gen. Calyptraa, Pileopsis. 

 Fam. 13. Patellida. Shell conical, with the apex turned forwards; 

 muscular impression horse-shoe-shaped, open in front. Foot as 

 large as the margin of the mantle. Kespiratory organ in the form 

 of one or two branchial plumes, lodged in a cervical cavity ; or of 

 a series of lamellae surrounding the animal between the body and 

 the mantle. 111. Gen. Patella, Acmcea. 

 Fam. 14. Dentalida. Shell tubular, symmetrical, curved, open at 



