THE VOYAGE OF H.M.S. CHALLENGER. 



Habitat. — OS" Nightingale Island, Tristan da Cunha, 100 to 150 fathoms. 



A beautifully delicate form, distinguishable by its very slender habit and the perfectly 

 cylindrical aspect of the branches, with the projecting cylindrical zooecia, the projecting 

 portion wholly oral. Its nearest ally would be Crisia holdsworthii. 



Division II.— INARTICULATA. 



. Centrifugines empdtes d cellules non operculees, d'Orb., Palseont. Fran?., 



p. 605 (pars). 

 Inarticulate sen affixw, Bk., Crag Polyzoa, p. 93. 

 Incrustata, d'Orbigny, Smitt. 



Character. — Zoarium continuous, not divided into distinct intemodes, fixed by a 

 contracted calcareous base, either erect and free, or immediately adnate upon foreign 

 bodies, and recumbent in whole or in part. 



Subdivision A. EEECTA. 

 Family II. Idmoneid.^, Busk. 



Tuhigeridx (pars), d'Orbigny, loc. cit, p. 698. 



Tuhuliporidx (pars), Johnst., Smitt, Hincks. 



Les Tubuliporiens (pars), Milne-Edwards. 



Idmoneidx, Bk., Crag Polyzoa, p. 94; Brit. Mus. Cat., pt. iii. p. 10; MacgilUv. 



Idmoneadx, Bk., Engl. Cyclopedia, art. Polyzoa. 



Horneridx, Hincks. 



Character. — Zoarium usually erect and rarely adnate, simple or branched ; branches 

 cylindrical, subcylindrical, or triangular, free or anastomosing. 

 The Family here contains the following genera : — 



1. Idmonea, Lamx^ 



I a. The zocecia aU disposed in alternate series on each side of the front of the 

 branches ; the innermost the longest. 



(1) Idmonea atlantica, E. Forbes. 



(2) Idmonea radians, Lamk. 



(3) Idmonea marionensis, Busk. 



(4) Idmonea australis, MacgiUiv. (PI. III. fig. 3). 



(5) Idmonea eboracensis, n. sp. (PI. III. fig. 4). 



