184 ITS STRUCTURE. 



groove exists around the exterior of the tentacular 

 disk. The latter is membranous, expanded, and ex- 

 cessively puckered or frilled with broad and deep 

 involutions, of which there are usually six or eight ; 

 the infoldings are sometimes simple, sometimes com- 

 pound ; in the latter case forming a semi-globose 

 head of fine slender tentacles, crowded together in 

 ■seeming confusion. 



When more carefully examined, the membranous 

 •disk appears to be really circular in outline ; the 

 mouth, an oval orifice with crenated lips, is not placed 

 on a cone ; delicate lines, as usual, radiate from it. 

 The innermost tentacles are placed at about half an 

 inch from the mouth (in a large specimen) ; these 

 are scattered irregularly and loosely ; others succeed, 

 more thickly, until towards the margin they become 

 a dense fringe, defying enumeration. The innermost 

 ones are stouter than the outermost : the length of 

 both varies much in specimens of the same size ; — 

 sometimes being not more than one-fourth of an inch 

 long, at others thrice this length. 



The whole texture is somewhat pellucid, especially 

 on the oral disk and the tentacles : the outer covering 

 of the body appears sub-coriaceous, though soft and 

 mucous. 



In Weymouth Bay this species is very common, 

 and still more abundant in the deeper water of the 

 ofiing ; both the dredge and the trawl constantly 

 bringing up single specimens and clustered groups. 

 The latter are sometimes very numerous, as many as 

 twenty being not uncommonly crowded on a single 

 oyster-shell. Of course such a group on so limited a 



