70 



sions: Cheilostomata, Cyclostomata and Ctenostomata, but in the first division also 

 within a series of widely different families and genera. Thus the net-like connec- 

 tion of the branches of the colony, so common in the family Reteporidae, we 

 also find in several Cyclostomata (Reticulipora, Reticrisina, Retihornera), in several 

 species of the family Adeonidae (e. g. in Adeona grisea, A. appendiculata, A.Wilsoni), 

 in the species oi Retiflustra as also in Membranipora sigillata^ and Petralia undata. 

 A colony consisting of cylindrical, or polygonal internodes generally connected 

 by flexible chitinous belts is found in such widely different forms as most spe- 

 cies of the genus Cellalaria, species of the genus Tubucellaria, the species of the 

 genera Farciminaria and Nellia, Microporina borealis, Schizoporella immersa and 

 species of the Ctenostome genus Flustrella (FI. dichotoma and Fl. Binderi). We 

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

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

 examples. This colonial form is the most prominent in the families Flustridae 

 and Bicellariidae, 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 Bicellariidae 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 species can appear in two or three diffe- 

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

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

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

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

 found it in the Throndhjem Fjord growing in free colonies of very difl^erent 

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

 Flmtra-like or Cellularia-like branches, and this author gives altogether 10 diffe- 

 rent forms of growth for this species. The 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 arctica, Thalamoporella Rozieri, Tb. 

 lioticha, Steganoporella Buski, St. magnilabris, St. trnncata, ^Lepraliai^ Pallasiana, 

 Smittina foliacea, Cheilopora sincera, Discopora pavonella, Disc, scabra, Disc, plicata, 

 Escharella labiata, Disc. Sarsii, Esch. rosacea, Porella struma, Porella compressa, 

 Porella Skenei, Smittina trispinosa, Sm. Lansborovi. 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 



' 103, p. 8. 



