370 DISCOVERY REPORTS 



This species, which was very accurately figured by MacGillivray, is distinguished 

 from Caber ea darwinii Busk by the characters of its scutum and cryptocyst. As in 

 C. boryi and C. zelandica, and in contrast to C. darwinii, there is a thickened, oblique 

 bar across the aperture to which the scutum is fused (Fig. 19 D). The scutum usually 

 has a small pointed distal lobe projecting over the thickened bar and a little point on 

 the proximal lobe, directed towards the stalk, though both may be lost. The proximal 

 lobe fills the opesia. Its lumen becomes narrower than that of C. darwinii, and curved, 

 constituting the "helicine mark" of MacGillivray. The cryptocyst is wide proximally 

 and usually granular, and in at least some of the zooecia in every colony has a crenulate 

 border. This border may be distinct in very young zooecia in which the granulation of 

 the surface of the cryptocyst has not yet appeared. On the other hand, it is sometimes 

 not discernible till the specimen has been treated with eau de javelle. Enlargement of 

 many of the frontal avicularia is common in this species, as in C. darwinii, and was 

 shown by MacGillivray in his fig. 1 . When the branch is seen in profile, these avicularia 

 may give a serrated edge to the frontal keel (Fig. 20 A). Some of the marginal avicularia 

 may also be slightly enlarged. There are usually two outer distal spines and one pedun- 

 cular spine. A second inner spine, which is also found in some specimens of C. darwinii, 

 is frequently present on young zooecia. 



In the New Zealand specimens from St. 934 and St. TN 91 the cryptocyst is rather 

 smooth, though wide as in typical specimens. A line of beading is present, but is not 

 always quite at the edge of the cryptocyst, so that it is not very conspicuous in frontal 

 view. A third outer spine is often present and the peduncular spine may be long and 

 stout. The vibracular chamber is rather smaller than usual, but it is not as small as in 

 C. boryi and the grooves are long. 



Two fragments from St. TN 144, belonging to this group of species, resemble 

 C. helicina in their scuta, enlarged frontal avicularia, small marginal avicularia and 

 moderate keel, and have long, stout peduncular spines like the other New Zealand 

 specimens ; but the cryptocyst is rather narrow and uniform in width and has a smooth 

 edge. Though small, the colonies are mature, having ovicells and being strongly 

 calcified. 



The Tertiary species figured as C. darwinii by MacGillivray (1895, pi. iii, fig. 10) 

 seems not to have had a bar across the aperture and is probably something different. 



A young colony of C. helicina (35.3.8.1), consisting of an ancestrula and two zooecia 

 is shown in Fig. 19 C. The ancestrula is similar in shape to that of C. darwinii but 

 smaller, and has only formed one vibraculum. The first zooecium has a strongly crenu- 

 lated border and a scutum of characteristic shape, but the lumen is rather restricted and 

 does not form a helicine mark, and the oral bar is set transversely to the longitudinal 

 axis of the zooecium, instead of obliquely. Each zooecium has a marginal avicularium. 



C. helicina is most nearly related to C. zelandica, but well-developed fertile colonies 

 of the two forms show pronounced differences. The branches of C. zelandica are flatter 

 frontally and stouter (cf. Fig. 20 A and B). The cryptocyst is very little, if at all, wider 

 proximally, and usually has a smooth edge. Rarely there is a little roughening or beading 

 near the base of the scutum. The frontal avicularia of C. zelandica are small, except for 



