POLYCERID^E. 69 



line of opaque white along each side of the back, which bend to- 

 wards each branchial tuft : head-veil with four longish linear 

 digitations : tentacles with a fasciculus of laminated or slightly 

 branched filaments, issuing from longish and narrow sheaths : 

 margins undulated and slightly mucronated : branchial pro- 

 cesses small, pinnate, 5 or 6 on each side, set on a slight pallial 

 margin : foot narrow, rounded in front. L. O7. 



HABITAT: Under large stones between tide-marks, Scar- 

 borough (Alder) ; Ilfracombe (Broderick) ; Channel Islea 

 (Ansted). 



Suborder III. ACANTHOBRANCHIATA. 



Gills plumose, surrounding the vent on the medio-dorsal 

 line. 



Family I. POLYCE'RIDJE. 



Mantle small or obsolete, spiculose, generally with marginal 

 appendages : dorsal tentacles variable : oral tentacles variable, 

 sometimes wanting: mouth with a denticulated prehensile 

 tongue or odontophore, and generally a spinous collar or horny 

 jaws. 



The Potyceridce, though resembling each other in general 

 form, are very variable in their other characters ; so that it has 

 been found necessary to constitute out of them several genera, 

 some of which contain only a small number of species. 



* Dorsal tentacles retractile within sheaths. 



Genus I. ^EGI'RUS *, Loven. 



BODY stout, convex, tapering behind, covered with large 

 tubercles : mantle indistinct, forming a veil over the head, and 

 a tuberculated ridge on each side: dorsal tentacles linear, 

 smooth, without laminae, retractile within lobated sheaths: 



* From uEgir, the god of the ocean in Scandinavian mythology. 



