398 MOLLUSCA. 



Fam. 2. Lamellariidae. Mantle more or less completely covering the shell. 

 Without operculum. Jaws fused dorsally. Lamellaria Montagu ; Onchidiopsis 

 Beck ; Velutina Blainv. ; Marsenina Gray. 



Fam. 3. Trichotropidae. Radula allied to that of Velutina. Trichotropis 

 Broderip. 



Fam. 4. Naricidae. Foot circular, carrying an epipodial lobe on each side ; 

 tentacles flattened ; shell naticoid, with a velvety periostracum. Narica Recluz. 



Fam. 5. Xenophoridae. Mineralogists, conchologists. Snout elongated ; 

 foot divided transversely into two parts, of which the posterior carries the 

 operculum. Shell trochiform, attaching foreign bodies (stones, shells) externally. 

 Xenophora Fischer. 



Fam. 6. Capulidae. Visceral sac and shell conical (patelliform), slightly 

 curved behind, usually with an internal plate ; without operculum ; columellar 

 muscle horseshoe-shaped. Capulus Montf. (Pileopsis Lam.), bonnet limpet ; 

 Grepidula Lam. ; Calyptraea Lam. , cup and saucer limpet ; Thy COL Adams. 



Fam. 7. Hipponycidae. Visceral mass and shell conical ; foot reduced, 

 may secrete a calcareous base. Hipponyx Defrance. 



Fam. 8. Littorinidae. Proboscis short, broad ; tentacles long, eyes at their 

 outer bases ; penis behind the right tentacle ; oviparous or viviparous ; radula 

 long ; shell turbinate, solid, operculum corneous. Marine or brackish water ; 

 mostly littoral. Littorina Ferussac, periwinkle ; Lacuna Turton ; Cremno- 

 conchus Blanford. Fossarus Philippi is allied here. 



Fam. 9. Cyclophoridae. Mantle-cavity without ctenidium, transformed into 

 a pulmonary sac. Tentacles long, filiform. Pedal ganglia elongated into cords. 

 Otocysts with otoconia. Operculum circular. Terrestrial. Pomatias Hartmann ; 

 P. obscurum S. Europe ; Cydophorus Montf. ; Cyclosurus Morelet ; Pupina 

 Vign. ; Cataulus Pfr. ; Cyclotus Guilding ; Pterocydus Benson ; Leptopoma Pfr. ; 

 Mcgalomastoma Guild. ; Craspedopoma Pfr. ; Diplommatina Bens. 



Fam. 10. Cyclostomatidae. Mantle-cavity pulmonary. Ctenidium absent. 

 Otocysts with otolith ; jaws absent ; deep median longitudinal groove in foot. 

 Operculum generally calcareous. Terrestrial. Cydostoma Drap. ; C. elegans 

 Miiller, Britain and temp. Europe. 



The Aciculidae (Acicula Hartm.), also terrestrial and found in Britain, are 

 allied here. 



Fam. 11. Truncatellidae. Looping snails. A monopectinate gill ; snout 

 long, bilobed ; foot very short. They walk by contracting the space between 

 the lips and foot. Found between tide-marks, survive many weeks out of water, 

 Truncatella Risso. 



Fam. 12. Eissoidae. Epipodial filaments ; operculigerous lobe with appen- 

 dages ; shell small, acuminate ; marine and brackish water. Rissoa Freminville ; 

 Litiopa Rang. 



Fam. 13. Hydrobiidae. Operculigerous lobe without filaments ; shell small, 

 acuminate. Brackish or fresh - water. HydroUa Hartm. ; Bithynia Gray ; 

 Lithoglyphus Miihlfeldt ; Pomatiopsis Tyron ; Bithynella Moquin ; Assiminea 

 Leach. 



The Skeneidae (Skenea Fleming) and Jeffreysiidae (Jeffrey sia Alder) are 

 allied here ; as also are probably the Homalogyridae (Homalogyra Jeffreys) and 

 the Choristidae (Choristes Carpentier). 



Fam. 14. Adeorbidae. Adeorbis S. Wood. 



