GASTEEOPODA. 191 



cavities ; gills surrounding the vent on the posterior part of the back, retrac- 

 tile into a cavity ; head with an oral veil, sometimes produced into labial 

 tentacles ; mouth with a lower mandible, consisting of two horny plates, 

 united near the fi'ont, and having 2 projecting points ; lingual teeth numer- 

 ous, central small, laterals similar, hooked and sometimes serrated (24-68 

 rows; 37-141 in a row; nidamental ribbon rather wide, forming a sjiiral 

 coil of few volutions (p. 50, fig. 29.) 



Sub-genus, Oncidoris (Bl. ?). D. bilamellata, Johnst. Back elevated, 

 tuberculose; gills non-retractile; oral tentacles fused into a veil; buccal 

 mass with a gizzard-like appendage ; lingual teeth 2 in each row. (A. and H.) 



D. scutigera {Villiersia) D'Orb. Rochelle; has the mantle more than 

 usually strengthened with calcarious spicula. 



The Dorids vary in length from 3 lines to more than 3 inches ; they 

 feed on zoophytes and sponges, and are most plentiful on rocky coasts, near 

 low-water, but range as low as 25 fms. They occur in all seas, from Nor- 

 way to the Pacific. 



GoNiODORis, Forbes. 



Eti/m. Gonia, an angle. Type, G, nodosa, PL XIII. fig. 2. 



Animal oblong; tentacles clavate, laminated, non -retractile; mantle 

 small, simple, exposing the head and foot. Spawn coiled irregularly. 



Distr. Norway, Brit. (2 sp.) Medit. China. Between tide-marks. 

 Tkiopa, Johnston. 



Type, T. clavigera, PI. XIII. fig, 3. Sijn. Psiloceros, Menke. 



Animal oblong; tentacles clavate, retractile within sheaths; mantle 

 margined with filaments ; gills few, pinnate, around or in front of the dorsal 

 vent. (A. and H.) Lingual teeth 8.1.8, or 8.0.8. 



Distr. Norway, Brit. Low-water — 20 fms. 

 ^GiRUS, Loven. 



Type, A. punctilucens, PI. XIII. fig. 4. Etym. ? Aix {aigos) a goat. 



Animal oblong or elongated, covered with very large tubercles ; no dis- 

 tinct mantle ; tentacles linear, retractile within prominent lobed sheaths ; 

 gills dendritic, placed around the dorsal vent. (A. and H.) Lingual teeth 

 17.0.17. 



Distr. Norway, Brit. (2 sp.) Prance. Litoral zone. 

 Thecacera, Fleming. 



Etym. Thehe a sheath, ceras a horn. Type, T. pennigerum, Mont. 



Animal oblong, smooth ; tentacles clavate, laminated, retractile ^Avithin 

 sheaths ; head with a simple frontal veil ; gills pinnate, placed round the 

 dorsal vent, and surrounded by a row of tubercles. (A. and H.) 



Distr. Brit. 2 sp. Lon. \ — \ inch. Found at low-water. 

 PoLYCERA, Cuvier. 



Etym. Polycera, many horns. Type, P. quadrilineata, PI. XIII. fig. 5. 



K 3 



