GASTEROPODA. 273 
Shell oval, conical, depressed, with the apex in front of the 
centre, and perforated ; surface radiated or cancellated; muscular 
impression with the points incurved. 
__ In yeryyoung 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. issurelia. (Wilton.) 
they chiefly inhabit the laminarian zone, but range downwards 
to 50 fathoms. For 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. 
Sub-genera. Pupillia, Gray. F. apertura, Born. (—hiantula, 
Lam.) Shell smooth, surrounded by a sharp white edge ; per- 
foration very large. Distribution, South Africa. Sissurellidea, 
D’Orbigny. F. hiantula, Lam. (=megatrema, D’Orbigny.). 
Shell cancellated; covered by the mantle of the animal. 3 
species. Cape and Tasmania. 
(Macroschisma, Sw.) FE. macroschisma, Pl. XI., 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 River. 
LIucapina, Gray. FF. elegans, Gray (—aperta, Sby.). Shell 
white, cancellated, margin crenulated ; covered by the reflected 
mantle. 3species. California. 
PUNCTURELLA, Lowe. 
Synonyms, Cemoria, Leach. Diadora, Gray. 
Type, P. noachina, Pl. XI., Fig. 3. 
Shell conical, eleyated, with the apex recurved; perforation in 
front of the apex, with a raised border internally; surface 
cancellated. 
Distribution, 6 (?) species. Greenland, Boreal America, 
N 3 
