GASTEROPODA. 273 



Shell oTal, conical, depressed, with the apex in front of the 

 centre, and perforated ; surface radiated or cancellated; muscular 

 impression with the points incurved. 



In very young shells the apex is entire and sub-spiral ; but as 

 the perforation increases in size, it encroaches on the summit 

 and gradually removes it. The key-hole limpets are locomotive ; 



Fig. 118. Fissurella. ("VVilton.) 



they chiefly inhabit the laminarian zone, but range downwards 

 to 50 fathoms. Eor dentition see Fig. 118. 



Distribution, 132 species. America, Britain, South Africa, 

 India, China, Australia, Upper California, Cape Horn. 



Fossil, 30 species. Carb. ; oolites — . Britain and France. 



Suh-genera. PupilUa, Gray. F. apertura. Born. (=hiantula. 

 Lam.) Shell smooth, surrounded by a sharp white edge ; per- 

 foration very large. Distribution, South Africa. Fissurellidcea, 

 D'Orbigny. F. hiantula. Lam. (=megatrema, D'Orbigny.). 

 Shell cancellated ; covered by the mantle of the animal. 3 

 species. Cape and Tasmania. 



{Macroschisma, Sw.) F. macroschisma, PI. XL, Fig. 2. 

 Anal aperture close to the posterior margin of the shell. The 

 animal is so much larger than its shell as to be compared to the 

 testacelle by Mr. Cuming. 



Distribution, Philippines and Swan Eiver. 



Lucapina, Gray. F. elegans. Gray (=aperta, Sby.). Shell 

 white, cancellated, margin crenulated ; covered by the reflected 

 mantle. 3 species. California. 



PuNCTtmELLA, Lowe. 



Sjnonyms, Cemoria, Leach. Diadora, Gray. 



Ttjpe, P. noachina, PL XL, Fig. 3. 



Shell conical, elevated, with the apex recurved ; perforation in 

 front of the apex, with a raised border internally; surface 

 cancellated. 



Distribution, 6 (r) species. Greenland, Boreal America, 



H 3 



