GASTEROPODA. 14J 



each, side, but no eyes ; foot small, secreting a float composed of numerou 

 cartilaginous air- vesicles, to the under surface of which the ovarian capsule 

 are attached. Lingual ribbon, rachis unarmed ; uncini numerous, simpl 

 (like scalaria). Branchial plumes 2. Sexes separate. 



Distr,., 6 sp. Atlantic, Coral sea. 



The ianthinse, or oceanic-snails, are gregarious in the open sea, whei 

 they are found in myriads, and are said to feed on the small blue acalephi 

 (velella}. They are frequently drifted to the southern and western Britis 

 shores, especially when the wind continues long from the S.W. ; in Swanse 

 bay the animals have been found quite fresh. When handled they exude 

 violet fluid from beneath the margin of the mantle. In rough weather the 

 are driven about and their floats broken, or detached, in which state they ai 

 often met with. The capsules beneath the further end of the raft have bee 

 observed to be empty, at a time when those in the middle contained youn 

 with fully formed shells, and those near the animal were filled with egg 

 They have no power of sinking and rising in the water. The raft, which : 

 much too large to be withdrawn into the shell, is an extreme modification < 

 the operculum. 



FAMILY XI. FISSURELLID.E. 



Shell conical, limpet- shaped; apex recurved ; nucleus spiral, often dii 

 appearing in the course of growth ; anterior margin notched, or apex perft 

 rated ; muscular impression horse-shoe shaped, open in front. 



Animal with a well-developed head, a short muzzle, subulate tentacle 

 and eyes on rudimentary pedicels at their outer bases ; sides ornamented wit 

 short cirri ; branchial plumes 2, symmetrical ; anal siphon occupying the ai 

 terior notch or perforated summit of the shell. Lingual dentition similar 1 

 trochus.* 



FISSURELLA, Lam. Key-hole limpet. 



Etym., diminutive offissura, a slit. 



Type, F. Listeri. PL XL, fig. 1. 



Shell oval, conical, depressed with the. apex in front of the centre ai 

 perforated ; surface radiated or cancellated ; muscular impression with tl 

 points incurved. 



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

 ration increases in size it encroaches on the summit and gradually removi 

 it. The key-hole limpets are locomotive ; they chiefly inhabit the laminaris 

 zone, but range downwards to 50 fms. 



Distr., 120 sp. America, Brit., S. Africa, India, China, Australia. T 

 California Cape Horn. 



* Fissurella is the best gasteropod for comparison with the bivalves ; its large gill 

 placed one on each side, and its symmetrical shell, pierced with a median orifice f 

 the escape of the out-going branchial current, are unmistakeable indications of horn 

 logic* with the lamelli-branchiata. See p. 48. 



