398 MOLLUSC A. 



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

 Without operculum. Jaws fused dorsally. Lamellar ia 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 troc-hiform, attaching foreign bodies (stones, shells) externally. 

 Xmophora 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 ; 

 Crepidula Lam. ; Calyptraea Lam., cup and saucer limpet ; Thyca Adams. 



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

 may secrete a calcareous base. Hippouyx 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 ; Crcinno- 

 conchus Bl an ford. 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 ; Cyclophorus Montf. ; Cyclosurus Morelet ; Pupina 

 Vign. ; Cataulus Pfr. ; Cydotus Guilding ; Pterocyclus Benson ; Leptopoma Pfr. ; 

 Meyalomastoma 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. Cyclostoma Drap. ; C. clegans 

 Mitller, 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 ; snoiit 

 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, 

 Truncatclla Risso. 



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

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

 Litiopa Rang. 



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

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

 Lithoylyplius Miihlfeldt ; Pomatiopsis Tyron ; Bitliynella. Moquin ; Assiminea 

 Leach. 



The Skeneidae (Skcnea Fleming) and Jeffreysiidae (Jeffreysia Alder) are 

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

 the Choristidae (Choristes Carpentier). 



Fam. 14. Adeorbidae. Adcorbis S. Wood. 



