GASTEROPODA. 



151 



perforation ; branchial plumes two. * — A few species ; 

 also fossil. 



The Philippine seas, and Northern Atlantic Ocean, 

 produce these small shells. R. noachina is the one most 

 commonly known. 



Fissurella. Brug. (Macroschisma Sw. ; Pupillia 

 Gray; Fissurellidea D'Orb.) — Shell oval, conical, the 



apex on the shorter or anterior 

 side of the shell having a round 

 or oval hole ; surface exteriorly 

 generally radiated, or rough. Ani- 

 mal, with a short muzzle, termi- 

 nating a tumid head, bearing two 



subulate tentacles, at the external 



Fissurella linibata. 



bases of which are the eyes, placed 



on rudimentary pedicles ; a range of numerous cirrhi round 

 the sides at the base of the very large foot ; mantle pro- 

 duced in front, with a fringe of cirrhi above its margin ; 

 anal siphon, in the form of a short, truncated membranous 

 canal, projecting from the apical aperture of the shell; 

 branchial plumes two.j — 122 species \; also fossil. 



The hole at the apex of this shell, serving as a passage 

 for the water from the branchiae of the Mollusc, which 

 are situated near it, differs in form, varying also with the 

 age of the shell, being in some species round, whilst in 

 others it is oblong, or resembling a key-hole. The shells 

 are generally thick and strong, and often delicately marked 

 with alternate dark and light colours. A few species are 

 found on the coast of England, in the same situations as 

 the Patella ; but none are so beautiful as those which are 

 found in the Tropics, some of which are very elegantly 



* Forbes's British Moll. f lb. \ Reeve's Iconica. 



Ij 4 



