291 



seen on figures of Ret. siiniosa Kirkp. ', Rel. novae zelandiae Waters- and Rhyn- 

 chozoon profundiim Mac Gill.'', as well as on the accompanying figures of Rhijnc. nnyii- 

 latam n. sp. (PI. XXIII, fig. 4 a). In those forms which have a strongly developed 

 peristome, the arch named is difficult to see from the frontal surface and to 

 examine it we must grind down the basal wall of the colony. This also applies 

 to the hinge-teeth. The rosette-plates seem to show great constancy, and in the 

 numerous species I have examined in this regard I have only found two in which 

 the rosette-plates had several pores. Thus, the distal wall in R. lata is provided 

 with a narrow, transversely oval rosetle-plale with a row of 3 — 5 pores and in 

 Rliijnc. an(jnlatum some of the rosette-plates may have two pores. The rosette-plates 

 in this species are exceptionally situated at the bottom of pore-chambers. The 

 ooecia also in spite of smaller differences show great agreement in their structure. 

 The peculiar layer of kenozocrcia, which covers the basal surface of the 

 free-growing colonies and is of the same nature as the expansion attaching 

 them to their under-layer, deserves closer description. With regard to this expan- 

 sion Smitt' has correctly recognised in Ret. elongata (Ret. Wallichidnd Busk), 

 that it consists of imperfectly developed individuals, and he has even found some 

 of them with an aperture. Hincks'' describes these individuals as ^aborted cells«, 

 but as I have already shown in my -Studies on Bryozoa< he" has in so far mis- 

 understood this expansion, that he regards it as the first formed i)ail of the 

 colony, whereas in reality it only arises after a number of ordinary zoa-cia have 

 been formed. It then gradually increases in extent with the further growth of the 

 colony. PI. X, fig. 1 c shows a beginning colony of R. Reaniana, which shows in 

 addition to a primary zooecium in the Memliranipora stage two fully developed 

 zooecia and the basal surfaces of two just beginning. Fig. 1 d on the other hand 

 shows a slightly older colony with a small radical expansion and in figs. 1 g and 

 1 h parts of this are magnified to a greater extent. Both show beginning keno- 

 zooecia on the growing margin the membranous roof of which has disappeared 

 in the previous boiling in caustic potash; their distal wall is provided with 1 — 2 

 small rosette-plates. If we examine the outer surface of a Retepora colonj' attached 

 to its under-layer, e. g. the colony of Retepora Reaniana figured on PI. X, 1 a, 

 which is attached by its radical expansion to a tube of Hijdroides norvetjica, we 

 see that the division into irregular, mostly avicularium-bearing areas shown by 

 this expansion is continued without inlerrui)tion or boundary on to the outer 

 side of the free part of the colony, with Ibis dilTerence, however, that these areas 



' 49a, p. 26i). - KlSi-, I'l, VII, fifrs. 1— 3. ■' KKS, I'l. II, lif^. 1."). ' 100, p. 200— 201, IM. .X.WIII, 

 lifj. 2:!2. ^ 22, p. .'ISS. '• 22, p. 394, fig. 18. 



19* 



