LECTURES ON MOLLUSCA. 89 



the mantle makes a spiked fringe, surrounding the gills and tentacles. 

 Palio has the veil slit in front. The tail of Trevelyna is lancet-shaped. 

 In Thecacera the mantle is obsolete, and the tentacles retractile. 



Family Tmopnxas. 



In this family the teeth are in very numerous rows, on a broad rib- 

 bon, but slightly hooked. The tentacles are retractile, within plaited 

 sheaths. Triopa has a beautiful set of palisades between the man- 

 tle and the foot, forming a fan-shaped row of ornamented tentacles 

 above the mouth. Other genera are Euplocamus and Plocamoceros. 

 AZgires has the tentacles smooth, and the teeth uniform. 



Family CERATOSOMIM. 



Ceratosoma has conical, spiny teeth in uniform rows, with a spiny, 

 somewhat retractile snout. The gills are retractile into a projecting 

 horn-shaped pouch ; but not the tentacles. 



In the following groups, the gills are scattered over the back of the 

 animal. 



Family TKITONIADJE. 



The Tritonias are elegant creatures, often large for the order, reach- 

 ing six inches in length. The gills are arranged in ornamented plates, 

 rising at regular intervals along the mantle-edge. The veil is large 

 and fringed : the teeth in very numerous rows, behind the horny 

 jaws ; and the fringed tentacles retractile within the sheath. They 

 live in shallow water, preying on zoophytes, &c. 



In Scyllma, the mantle-margin is produced into flaps, bearing the 

 gills on their inner edge. The foot is narrow, and grooved for clasp- 

 ing floating sea-weeds, on which they are borne about. 



Family TETHYADJE. 



The Tetliys has an enormous flat veil, as large as the body, and copi- 

 ously fringed at the edge. Although it has no teeth or jaws, frag- 

 ments of crabs and shells have been found in its fleshy gizzard. 



Family DENDRONOTIM. 



In the Dendronotids and the groups which follow, the stomach and 

 liver are curiously spread out and branched. Dendronotus has a beau- 

 tiful row of tree-like gills, along the middle of the back. The tongue- 

 ribbon is broad, with very numerous series of serrated lancet teeth. 

 Bornella and Lomanotus are other genera. 



Family PEOCTONOTIDJE. 



In Proctonotus and Janus the gills look like the stamens of a flower, 

 copiously arranged round the mantle edge. There are strong horny 

 .jaws, and the tentacles are not sheathed. 



