236 LECTURES ON MOLLUSC A. 



borhood some time before lie can dredge and examine the forms which 

 belong to each fauna. As they do not preserve their shapes in alcohol, 

 and leave nothing that can be kept in cabinets or impressed on strat- 

 ified rocks, they can scarcely be understood without reference to fig- 

 ures; and therefore only the principal groups will be here described. 

 The student is recommended to examine the plates of Alder and Han- 

 cock for the British, and of H. and A. Adams for the exotic tribes. 



In the first group of families, the gills are on the back, near the 

 tail, and surrounding the vent. The skin is leathery, of a spongy 

 texture, and stiffened with minute darts. 



Family Doridje. (Sea Lemons.) 



The Doris and its allies have tree-like gills, with the vent in the 

 middle. The teeth are in very numerous longitudinal series, resem- 

 bling the Bullas. They feed on zoophytes and sponges, and lay their 

 eggs in a spiral ribbon, attached on one side. The body is convex; 

 the mantle large, but plain at the sides; and the back tentacles can be 

 drawn into pouches. The gills can be drawn into a general cavity. 

 The genera Glossodoris, Ghromodoris, Actinodoris, Asteronotus, Acti- 

 nocydus, Atagema, and Dendrodoris are characterized by differences 

 in the shape of the gills, tentacles, and mantle. In Hexabranclius 

 and Heptabranchus, each gill has a pouch to itself; the circle in the 

 latter not being complete. 



Family Onchidoridje. 



In Onchidoris, the gills are not retractile, and the back tentacles are 

 laminated. The tongue is narrow, with two rows of large teeth (as 

 in Philine) and buttresses outside. The other genera are Acantho- 

 doris and Villiersia. 



Family GoxiODORiDiE. 



The Goniodorids have a flattened, angular body. The mantle does 

 not reach the head and foot, and the gills are not retractile. The 

 tongue-ribbon is narrow, with four series of spines. The Red Sea 

 Brachichlanis has the tentacles in front of the mantle. 



The lovely Idalias have the mantle almost obsolete, but produced 

 into four false tentacles in front of the true ones, and smaller ones 

 round the gills. In the very curious Ancida, ^afterwards named '''Mi- 

 randa/') the mantle degenerates into a semi-circular palisade to pro- 

 tect the beautiful bunch of branching gills. The tentacles are elegantly 

 folded at the ends,, and below are fringed with spreading feelers. This 

 smooth, transparent, slug-shaped creature, only yet known in the 

 German ocean, glides along, with a spreading moustache above its 

 mouth, carrying its living flower-basket on its back. 



Family Polyceridje. 



The " many-horned" Nudibranchs differ from the last family in 

 having twelve or sixteen teeth on the tongue-ribbon. In Polycera, 



