70 



sions: Clieilostoimitd, Ciicldstoinald and (Itenoslomatd, ))iil in the first division also 

 within a scries of widely dilTerent families and genera. Thus the nel-like connec- 

 tion of the hranches of the colony, so common in the family Retci)t>ri(l(ie, we 

 also find in several Ciiclosloinata {ReiicuUimni, livlicrisina, Retihornerd), in several 

 species of the family AdeonUUie (e. g. in Ailcona (irisca, A. dppemliculitld, A.WUsnni), 

 in the species of Ri'lijhixlra as also m Mciiihrdniixira sigilldtd^ i\nd Pelrdlia iiiidata. 

 A colony consisting of cylindrical, or })olygonal internodes generally connected 

 by flexible chitinous bells is found in such widely difTerent forms as most spe- 

 cies of the genus Celhildrid, species of the genus Tnhiuelldrid, the species of the 

 genera Fdrciniiiiaria and Nellia, Microporiiia borcdlis, Schizuporella ininiersd and 

 species of the Ctenoslome genus Fliistrella (Fl. dichotoma and Fl. Binder!). We 

 have here only mentioned some of the most peculiar forms of colony; for of the 

 more common, e. g. free colonies with Ihxt branches, we might cite numerous 

 examples. This colonial form is the most prominent in the families Fliislri<lae 

 and Bicellariidde, and the particular stress which has been laid on the colonial 

 form, as far as the first family is concerned, has, as we shall see later, resulted 

 in several members of the family Bicellariidde being described under the name of 

 Flustra. Just as the same form of colony may on the one hand appear within 

 widely different families and genera, it is on the other hand not always constant 

 even within the species, and numerous sj)ecies can appear in two or three difTe- 

 rent forms of growth. The colonial form can therefore not at all he used as a 

 specific character with certainty. One of the species which otTers the most 

 striking example of variation in regard to form of growth is Electra jiilo.sd. While 

 this sjiecies is at our coasts only known in an incrusting state, Norman has 

 found it in the Throndhjcm Fjord growing in free colonies of very difTerent 

 shape, sometimes with tiie zooecia in one row, sometimes in two, sometimes with 

 F/iis/ra-like or (^elliilarid-Vike branches, and this author gives altogether 10 diffe- 

 rent forms of growth for this species. Tiie following may be mentioned as ex- 

 amples of species, which appear not only incrusting, but also in free, foliaceous, 

 one- or two-layered colonies: Membranipora arcticd, ThaUimoporeUa Rozieri. Th. 

 liotichd, SteijctnofMrella Biiski, St. mafinilahris, St. tnincala. Leprdlid- I'dlldsiana, 

 Smittiiid folidceu, C.heilopura sinceru, Discupora pavonellu, Disc, scdbrd, Disc, plicata, 

 Escharella lubiatu. Disc. Sarsii, /i.sc/i. rosacea, Porella struma, Porella compressa, 

 Porelld Skcnei, Smiltiiia Irisfiino.sd, Sin. Ldnsborovi. The question, how far it would 

 be correct in any case to limit a species, genus or family from one or .several 

 others only on the basis of difference in the colonial form, must therefore be 



' io:i. p. s. 



