At /, in fig. 1 6, there is the edge of a lamella which is so prominent as to suggest 

 that it was for a time the edge of an orifice (the lamellae between f and b have not been 

 indicated in the figure). There can be no doubt that this was the case ; and it will readil\- be 

 seen that at this time the orifice was produced into the principal filamentous process r, which 

 soon gave off the lateral branch d\ while a third process e was formed at the opposite side 

 of the orifice. With the increase in the length of the coenoecial tube the process e has been 

 left unconnected with any orifice. The principal growth has taken place along c, which has 

 doubtless increased meanwhile by the addition of new cones to its ape.\. The terminal orifice 

 «, with its process c, now has a close resemblance to a peristome of C. levinseni. It consists 

 almost entirely of primary lamellae, namely those of the mid-rib, and those of the rest of the 

 tube. Secondary lamellae are at present but slightly developed. 



Should further additions be made to the orifice b it is highly probable that they would 

 take place along the process d, and a bifurcation of the coenoecium would thereby result. 

 Fig. 1 5 shews that a considerable number of peristomial filaments may be developed in con- 

 nexion with a single orifice. 



Fig. 54 represents a longitudinal .section through an orifice, with several peristomial 

 filaments, of C. gracilis \ while fig. 55 represents part of a transverse section through the 

 coenoecium, more highly magnified. The figures both shew a considerable development of 

 secondary lamellae on the inner side of the primary lamellae. 



C. sibogae. (PI. II, figs. 17, 18. PI. IX, figs. 102, 103). 



It must be remembered that the colony here described under this name contains male 

 and neuter individuals, no females being present. It is thus necessary to consider the possibility 

 that it may be the male form of C. gracilis. 



The neuter zooids of C. sibogae are perfectly characteristic Cephalodiscus individuals 

 except for the absence of functional reproductive organs. It can hardly be doubted that they 

 take an important share in the secretion of the coenoecium, though I see no reason why the 

 extraordinary male individuals should not contribute to its growth. But even taking account of 

 this possibility, there seems no obvious reason why the characters of the coenoecium should 

 differ to any great extent in the two sexes of the same species. The fact that there are definite 

 differences in the coenoecia of the forms here described under the names of C. gracilis and 

 C. sibogae is one of my principal reasons for regarding them as belonging to distinct species. 



The coenoecium of C. sibogae consists of two very different parts: — (I) a denser 

 portion which forms a continuous expansion over the rock on which it grows; (II) a series of 

 upstanding tubes, fringed with numerous peristomial filaments, and arising from the basal 

 encrustation (PI. I, fig. 2). 



The cavity of the coenoecium is continuous, that of the erect tubes passing into those 

 of the basal encrustation. It is a remarkable feature of this colony that the zooids are nearly 

 all retracted into the latter, so that the erect tubes are for the most part completely 

 without zooids. 



