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i. Alcyonidium polyoum Hassall. (PI. III, fig. i). 



Sarcochitum polyoum Hassall, 1841, "Suppl. Cat. Irish Zooph.", Ann. Mag. Nat. Hist. VII, p. 484. 

 Alcyonidium mytili Dalyell, 1848, "Rare and Remark. An. Scotland", II, p. 36, PI. XI. 



figs 1 — 14. 

 Alcyonidium mytili Hincks, 1880, "Hist. Brit. Mar. Pol.", p. 49S, PI. LXX, figs 2, 3. 

 Alcyonidium mytili Levinsen, 1894, "Zool. Danica", IX, "Mosdyr", p. 81, PI. VII, figs 33 — 37. 

 Alcyonidium mytili Silbermann, 1906, u Unt. Alcyonidium mytili", Arch. f. Naturg., Jahrg. 72, 



Bd I, p. 265, Pis XIX, XX. 

 Alcyonidium mytili Osburn, 1912, "Bry. Woods Hole", Buil. Bur. Fisheries, XXX, p. 251, 



PI. XXVIII, figs 74, 740. 

 Alcyonidium mytili Sumner, Osburn and Colc, 191 3, "Biol. Surv. Woods Hole", Buil. Bur. 



Fisheries, XXXI, Pt I, pp. 108, 109; Pt II, p. 606. 



The following records, without description or figure, may also be noticed : 



Alcyonidium mytili Robertson, 1900, "Bry. Harriman Alaska Exp.", Proc. Washington Acad. 



Sci., II, p. 329. 

 Alcyonidium mytili Calvet, 1904, "Bryozoen", Hamburg. Magalhaensische Sammelreise, p. 38. 

 Alcyonidium mytili Thornely, 1905, Herdman's "Rep. Pearl Oyster Fisheries Gulf of Manaar", 



Publ. by the Roy. Soc, Suppl. Rep. XXVI, p. 127. 



Kirkpatrick's A. mytili, from Victoria ("Pol. Port Phillip", Ann. Mag. Nat. Hist., (6) 

 II, 1888, p. 17, PI. II, figs 6, 6a) does not appear to me to belong to this species. 



It is probable that Sarcochitum polyoum Hassall, 1841, is the form assumed by old 

 colonies of A. mytili. If this be the case, Hassall's name has the priority, as has been pointed 

 out by Osburn (191 2). Duerden *) has recorded A. mytili from Dublin Bay, and considers that 

 it is identical with Hassall's species, from the same locality. Silbermann (1906, p. 266), in a 

 recent study of A mytili, comes to the conclusion, however, that this species is distinct from 

 A. polyoum. 



Murray Islands, Torres Straits, 15 — 20 fathoms, on Euthyris obtecta Hincks. Mus. Zool. 

 Cambridge, Reg. Sept. 1, 1900; now transferred to the British Museum. 



Zoarium forming a thin film, the interzooecial septa very distinct. Zoocia more or less hexa- 

 gonal, averaging about 450^ in length ; the orifice on a low papilla which is not quite terminal. 



I do not teel certain that the present form is correctly referred to the European species ; 

 but there is nothing in the characters given above to forbid this association. 



The single specimen under consideration forms an extremely thin, transparent film 

 encrusting a part of the frontal surface of a colony of Euthyris obtecta. lts interzooecial septa, 

 which are very distinct, have been developed without any relation to those of the Cheilostome 

 on which it is growing. Some of them cross the opercula of the Euthyris, the corresponding 

 polypides of which have degenerated, although they are present beyond the growing margin 

 of the Alcyonidium : - - indicating that the degeneration has been the result of the occlusion 

 of the orifices. 



The orifice of the Alcyonidium is of the usual type, being ver) - small and circular, or 

 transversely oval, in the retracted condition, and being situated at the summit of a low papilla, 







1) Duerdex, J. E., 1894, "Notes Mar. Idv. Rush, Co. Dublin'', Irish Nat., III, p. 232. 



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