7 S EXPEDITION ANTARCTIQUE BELGE 



surface of the dorsal layer there are vibices, which are lines without any relation to the zocecia, 

 not being merely surface lines but extending through the dorsal layer. Fig. 6a taken from 

 a préparation of R. crassa B. shows this structure which is gênerai. It will be seen, that 

 the interior of thèse vibical divisions is formed of parallel lines, and from the broken surface 

 (PI. VI, figs. 6a, b) it would appear as if the neighbouring areas dovetail into one another. 



Levinsen (') considers the oral bow, which I hâve previously alluded to as a «shclf», 

 is of great classificatory value, and says it occurs in différent families, and is gênerai in 

 Reteporidœ. The genus is placed by Levinsen in his Camarostega, and the ovicell is hyper- 

 stomial. 



Hincks ( 2 ) lias correctly described the base of Retepora, but I cannot agrée with him 

 in his description of the order of its formation, as of course from one zoeecium grow the zocecia 

 from which the colony is further developed and in a very early stage, the zoœcia throw 

 out the expanded crust referred to. A similar mistake has been made concerning the radicles 

 of other rooted forms, for fresh radicles are being constantlv formed as the colony grows ; 

 and in the same way the basai part of Retepora increases as strength is required. The attach- 

 ment of a considérable number of the Chilostomatous Bryozoa is similar, being formed by a 

 subséquent growth in no way resembling the zoœcia ; but there are some species of Bryozoa, 

 in which at first the zoarium is adnate, having zocecia like those in the erect portion, which 

 of course grows from the adnate part, as seen in Smittia gelida nov. Sometimes Retepora throws 

 out one or more fresh attachments, and when this is to a body near to the zoarium, then the 

 calcareous growth is similar to that of the base of the Reteporœ generallv. This is seen in 

 R. hippocrepis nov. (PL VI, fig. 10a). 



No gênerai considération of Retepora would be complète without taking into account a 

 massive bilaminate species without any reticulation, occurring off South Africa and which came 

 into my hands through Miss Jelly's kindness, after my paper on Retepora ( 3 ) was published, 

 and since then I hâve intended to describe it. Howevcr I now give a figure of one zoœcium, 

 and the operculum (PI. VI, figs. 8a, b, c, d) hoping sometime to give fuller figures. It will be 

 seen that it is of the R. fissa type having a fissured raised ovicell, the zoœcia are distinctly 

 separated, and to each zoœcium there are four or more small raised circular avicularia, with 

 semicircular mandibles ; below the aperture there is a small labial avicularium, with semicir- 

 cular mandible ; there is a peristomial slit, and on the surface of the zoœcia there are nume- 

 rous large pits as well as the avicularia. The operculum is wide below, and becomes narrower 

 towards the distal end, being similar in shape to the operculum of R. protecta sp. nov. 



Busk also refers to a bilaminate form in his «Challenger Report », p. 114, but he says it 

 belongs to the R. tessellata group, and it does not seem probable that he could hâve considered 

 the S. African form as having chitinous organs similar to those of R. tessellata. Busk says 

 that the spécimen is in the Oxford Muséum, though unfortunately he does not state where it 

 was from. I went to Oxford, for the purpose of seeing this interesting species, but it could 

 not be found. 



A most interesting point in connection with m}' South African species is that R. granulata 



(1) Studies on Bryozoa. [Vidensk. Medd. fra d. Naturh. Foren., Kjôbenhavn, 1902, p. 19.) 



(2) Hincks, British Marine Polyzoa, p. 38g. 



(3) Linn. Soc. Journ. Z00L, vol. XXV, pp. 255-272, pi. 6-7, 



