1. IDMOXEA. 11 



Crisia (pai's), D'Oibif/ny, Stoliczku, Sttiiit. 



Retepora (pars), Go/dftiss, Lamk. 



Diastopora (pars), Michelin. 



Tubiilipora (pars), Lamk. 



Tubulipora, subgen. Idmouea, Smitt, I. e. p. 398. 



a. Branclves mhtriangtdar or angular in front. 

 1. Idmonea atlantica, E. Forbes. (Plate IX.) 



Zoariuni irregularly branched, usually more or less ia one plane ; 

 branches triangular ; cells 1-4 or 5 in each series, the innermost 

 the longest ; dorsal surface of branch not perforate ; peristome entire. 



Idmonea radians, V. Beneden, I. c. p. 646, pi. xii. figs. 4, 6. 



? Idmonea coronopus, Defr. Did. d. Sc. Nat. xxii. p. 565 ; U Orb. ; 



M.-Edtcards, I.e. pi. 8." fig. 4. 

 Idmonea atlantica, Smitt ; Johnston, 1. c. p. 278, pi. 48. fig. 3 (bad) ; 



Oral/, Cat. Rad. p. 141 ; Sars, Seise Lof. Finm. p. 145 ; Landsb. ; 



Go.sse, Mar. Zool. part 2, p. 8. fig. 3; Busk, Ann. Nat. Hist. ser. 2, 



vol. xviii. p. 34, pi. 1. fig. 6, a-e ; id. Quart. J. 3ficr. Science, vi. 



p. 128, pi. xviii. fig. o ; id. Rep. Brit. Assoc. 1859, Trans. Sect. 



p. 146 (var. tenuis) ; Smitt, Floridan Bryozoa, p. 6, pi. ii. fig. 7. 

 ? Idmonea angustata, Z)' Orb. Pal. Fran^. p. 731 . 



Ilab. Arctic seas and coasts of Norway and Finmark ; Shetland 

 {Bctrlee), Var. tenuis. North Atlantic ; Gulf of Florida ; Madeira. 



2. Idmonea radians, Lamk. (Plate VII. figs. 1-4.) 



Zoarium usually procumbent, stipitate, sometimes suberect ; 

 branches dichotomous, radiating more or less regularly in a circular 

 form from the centre, very angular in front ; dorsal surface perfo- 

 rated ; cells 1-4 in each series, the innermost the longest ; aperture 

 (when quite perfect) bilabiate. 



Retepora radians, Lamk. Hid. d. An. s. Vert. 2nd ed. p. 279; D'Or- 



biyny, I. c. p. 731. 

 ? Hornera radiata, Blainville, Man. d'Actin. p. 419. 

 Idmonee rayounante, M.-Edw. I. c. p. 25. 



Hab. Australian seas (abundant) ; New Zealand. 



There can be no doubt of the distinctness of /. radians from the 

 northern form, /. atlantica, nor of its occurrence in the seas of New 

 Holland, of which M. M. -Edwards appears to have had some doubt. 



Its peculiar and very beautiful, regular habit, when in perfection, 

 delicacy of structure, size, and, above aU, its punctured dorsal sur- 

 face, at once suiRce to distinguish it. In all the instances I have 

 seen, in this species more especially, the zoarium arises from a short 

 iipright stem, which spreads out at bottom into a small circular disk 

 of attachment upon shells and stones. Idmonea atlantica is less 

 regular in form, but sometimes affects a stelliform procumbent 

 figure ; and, although the growth of the tubular cells is confused at 

 the bottom, I have never myself seen it to aiise from what could 

 properly be termed an adnate growth like Criserpia or TuhiJipora. 



B 2 



