GASTEROPODA. 277 



Type, C. fornicata, PI. XI., Fig. 16. 



Synonym, Crj^ta, Humph. 

 • Shell oval, limpet-like ; with a posterior, oblique, marginal 

 apex ; interior polished, with a shelly partition covering its 

 posterior half. 



The crepidulce resemble the fresh- water naviceJke in form ; 

 but the internal ledge which mimics the columella of the nerite, 

 is here the basis of the adductor muscles. 



They are sedentary on stones and shells, in shallow water, and 

 are sometimes found adhering to one another in groups of many 

 successive generations. The specimens or species which live 

 inside empty spiral shells are very thin, nearly flat, and 

 colourless. 



Distribution, 54 species. West Indies, Honduras, Mediter- 

 ranean, West Africa, Cape, India, Australia, West America. 



Fossil, 14 species. Eocene — . Prance, North America, and 

 Patagonia. 



PiLEOPSis, Lam. Bonnet-limpet. 



Etymology, pileos, a cap, and opsis, like. 



Synonyms, Capulus, Montf. Brocchia, Bronn. 



Type, P. hungaricus, PI. XI., Fig. 17, P. militaris, PI. XI., 

 Fig. 18. 



Shell conical; apex posterior, spirally recurved; aperture 

 rounded ; muscular impression horse-shoe shaped. 



Animal with a fringed mantle-margin ; lingual teeth like 

 calyptrceo,. 



P. hungaricus (the Hungarian-bonnet) is found on oysters in 

 6 to 15 fathoms water ; more rarely as deep as 80 fathoms, and 

 then very small. P. militKiris is extremely like a velutina. 



Distribution, 8 species. West Indies, Norway, Britain, 

 Mediterranean, India, Australia, California. 



Fossil, 20 species. Lias — . Europe. 



Sub-genus. Amathina, Gray. A. tricarinata, PI. XL, Fig. 19. 



Shell depressed, oblong; apex posterior, not spiral, with 

 three strong ribs diverging from it to the anterior margin. 



Platyceras, Conrad (acroculia, Phil.). P. vetustus. Carb., 

 limestone. Britain. 



Fossil, 20 species. Devonian — Trias. America, Europe. 



Metoptoma, Phillips. M. Pileus, Ph. 



Shell limpet-like, side beneath the apex truncated, resembling 

 the posterior valve of a chiton. 7 species. Carb. limestone. 

 Britain. 



