800 MANUAL OF THE MOLLUSCA. 
GONIODORIS, Forbes. 
Eiymology, 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. 
Distribution, 26 species. Norway, Britain (2 species), Medi- 
terranean, China. Between tide-marks. 
TRIOPA, Johnston. 
Type, T. clayiger, Pl. XTIL., Fig. 3. 
Synonym, Psiloceros, Menke. 
Animal oblong; tentacles clavate, retractile within sheaths; 
mantle margined with filaments; gills few, pinnate, around or 
in front of the dorsal yent. (A. and H.) Lingual teeth 8.1.8, 
or 8.0.8. 
Distribution, 3 species. Norway and Britain. Low water— 
20 fathoms. 
ZAGIRUS, Loyén. 
Type, Zi. punctilucens, Pl. XIII., Fig. 4 
Etymology, ? aix (aigos), a goat. 
Animal oblong or elongated, covered with very large tubercles; 
no distinct mantle; tentacles linear, retractile within prominent 
lobed sheaths; gills dendritic, placed around the dorsal vent. 
(A. and H.) Lingual teeth 17.0.17. 
Distribution, 3 species. Norway, Britain (2 species), France. 
Littoral zone. 
THECACERA, Fleming. 
Etymology, theke, a sheath, ceras, a horn. 
Type, T. pennigerum, Mont. 
Animal oblong, smooth; tentacles clavate, laminated, re- 
tractile within sheaths; head with a simple frontal -yeil; gills 
pinnate, placed round the dorsal vent, and surrounded by a row 
of tubercles. (A. and H.) 
Distribution, Britain, 2 species. Length, 4—} inch. Found 
at low water. 
POLYCERA, Cuvier. 
Etymology, poiycera, many horns. 
Type, P. quadrilineata, Pl. XIII., Fig. 5. 
Animal oblong or elongated; tentacles laminated, non- 
retractile, sheathless; head-vyeil bordered with tubercles or 
