76 SIDNEY F. HARMER. 



pyriform shape. I have found mature colouies of this type 

 commonly in at least three of the species described in the 

 present paper, namely in T. phalangea, T. flabellaris 

 (fig. 4), and T. aperta (fig. 2). 



In other cases the transverse growth of the terminal mem- 

 brane is more active, and the flabelliform character becomes 

 more marked (figs. 1 and 5), its lateral edges commonly 

 growing proximally so as more or less to encircle the primi- 

 tive disc. This flabelliform shape typically occurs in well- 

 grown colonies of T. flabellaris and T. aperta. In other 

 species the terminal membrane commonly divides at an early 

 stage, so that there is a cessation of growth between the two 

 parts of the divided membrane. The colony then grows into 

 two lobes, which usually diverge from one another. This 

 form of growth is well indicated by Pallas (33, p. 248) in his 

 original account of T. liliacea (= T. serpens, auctt.). 

 Colonies of this species, as well as those of T. phalangea 

 and T. plumosa, often become mature in this condition ; but 

 in all three species further divisions of the terminal mem- 

 brane^ usually take place, the colony thus becoming variously 

 lobed. In T. liliacea alone of the forms described in this 

 paper, there is in many cases a marked tendency for the lobes 

 to become free and erect; and an Idmonea-like form thus 

 results. 



The common basal part of a colony consists of a mass of 

 pyramidal tubes with pointed proximal ends, the arrangement 

 being comparable with that of a honeycomb, all the " cells'' of 

 which look in one direction, represented in Tubulipora by 

 the growing margin of the lobe. The base of the colony, or 

 basal lamina, is the sum of the lower walls of the more 

 proximal parts of the zooecia. It is completely adherent to 

 the substratum in many species of Tubulipora, but it may 

 grow out freely from it, and the colony thus becomes erect. 

 Each zooecium is developed at the growing edge by the forma- 

 tion of a new radial septum in connection with the basal 



1 A commencing division of the terminal membrane is indicated on the 

 right side of fig. 1. 



