92 THE VOYAGE OF H.M.S. CHALLENGER. 



of the spicules; length to breadth in mm.: — Rudimentary opercular scales; 0-27-0 -2. 

 Calyx and outer layer of coenenchyma scales, 0-2-0-2 ; 0-12-0-15 , 013-012; 0-12- 

 0-18 ; 0-14-0-15 mm. The deep spicules of the coenenchyma are jagged, often 

 branched spicules of irregular form, or small, triangular, thick discs with prominences, 

 0-17-0-12; 0-09-0-1 ; 008-0-05 mm. The small scales which cover the calyces are 

 not capable of giving to the latter the rigidity found in other Primnoids, hence the 

 calyces possess a soft, yielding structure. 



Habitat. — Station 145a, off Prince Edward Island; depth, 310 fathoms; bottom, 

 volcanic sand. 



Family IV. M u R I c E i D ^E, Verrill. 



Muriceadx, Studer. 

 In this family we include those Holaxonia with a horny axis in which the 

 coenenchyma and the polyps contain large and variously formed calcareous spicules ; 

 the projecting points and spines of these latter giving to the colony a peculiar, irregular, 

 roughened appearance. The polyps consist of basal portions armed with spicules, 

 the calyx ; of a naked portion which contains the oesophageal tube, the oesophageal 

 portion ; and the oral disc with the tentacles ; the latter contain spicules in their basal 

 portions which rest upon a collerette of spicules lying peripherally under the tentacular 

 crown. In repose the tentacles are folded inwards so that the spicules of their bases 

 lie together forming a covering over the mouth, while the whole oesophageal portion of 

 the polyp is folded into the body-cavity. The spicules of the tentacles thus form a 

 covering over the oral region. The chief characteristic of the family therefore lies in 

 the peculiar habit of the polyps. In repose, the tentacles are always folded together 

 over the oral disc (which becomes a little contracted) by which the basal portions 

 of the tentacles, armed with spicules, form an operculum over it ; the infolding of the 

 oesophageal portion brings this operculum over the oral portion ; sometimes, as in 

 Muricea and Elasmogorgia, draws it into the body-cavity itself. This infolding takes 

 place indeed in a very different degree, as wiU be seen, according to the genus. It 

 occurs in a minimum degree in Acanthogorgia, where the polyp body is very much 

 elongated and indeed only invaginates the oral disc ; but here, as in some sort a 

 protection of the soft parts of the body, the edges thereof are armed with sharp 

 spicules. It occurs at a maximum in Muricea and Elasmogorgia where the tentacular 

 covering is even withdrawn into the body-cavity. 



The family of the Muriceidfe embraces the genera and species included by Studer 

 in the IMuriceadse as a subfamily of Primnoidae ; ^ it is only lately that Verrill has 

 rightly raised the subfamily to the rank of a family.^ 



» Monatsber. d. k.preuss. Akad. d. Whs. Berlin, 1878, p. 641. » Bull. Mus. Comp. Zool, vol. xi. No. 1, 1883. 



