CABEREA 365 



noides. Philipps (1899, p. 441) noted differences between the specimen from Brazil 

 (90. 1 .30. 13), which appears to have been correctly determined as C. retiformis, and 

 her specimens from Lifu which have proved to belong to C. clypeata and C. pecten var. 

 scutata (see Harmer, 1926, pp. 387, 389). 



Caberea Lamouroux, 18 16 



Two much-discussed groups of species of Caberea are represented in these collec- 

 tions, namely, the C. darwinii group and the C. boryi group. In C. darwinii the outer 

 distal border of the scutum typically meets a little projection from the outer border of 

 the opesia so that the operculum is framed, and there is usually another small condyle- 

 like process at the base of the stalk of the scutum (Fig. 21 A). 1 In C. boryi there is a 

 complete calcareous bar across the orifice underlying the distal border of the scutum 

 which is fused to it (Fig. 19 B). The bar has a suture, and it seems probable that it 

 is formed by the fusion of outgrowths equivalent to the condyle-like processes of 

 C. darwinii. The presence of a bar is associated with other characters apparently of 

 systematic value, and, although one can imagine the bar being developed secondarily 

 as the zooecium grows older, I have in fact found that it is laid down at a very early 

 stage in the development of the zooecia of those forms in which it is present, and I have 

 seen no tendency to its subsequent development in other forms. I therefore conclude 

 that the presence or absence of a bar is a character of systematic importance. 



The C. darwinii group as I understand it extends over a wide area, and the characters 

 appear to intergrade in correlation with climatic conditions so that, despite the dif- 

 ferences, in size and other characters, of the extreme forms on the fringes of the area, 

 there may only be one species (see pp. 377, 383). 



In the C. boryi group, on the other hand, I have given reasons for recognizing three 

 species, C. boryi, C. helicina and C. zelandica, whose differences are not correlated with 

 distribution. C. boryi has a wide range from the Mediterranean (perhaps England) to 

 Australia ; the other two species are known from Australia and New Zealand, and from 

 New Zealand and Juan Fernandez respectively. 



A frontal keel is a conspicuous feature of some biserial forms of Caberea, and most 

 species are also more or less keeled basally. The frontal keel is formed by the oblique 

 development of the frontal surface of the zooecia, so that they slope away from the mid- 

 line of the branch. The basal keel is formed partly by the convexity of the basal surface 

 of the branch, but chiefly by the projection of the vibracular chambers. The extent to 

 which a branch is keeled, both frontally and basally, is best estimated from a lateral view, 

 as can be seen in Figs. 20 A, B, 21 C, 25 D. In Fig. 25 D, for instance, there is a pro- 

 nounced basal keel, while the frontal surface, being rather flat, is seen in foreshortened 

 view. In Fig. 20 A the basal keel is less marked, but the frontal surface is so strongly 

 keeled that the opesia and cryptocyst are in almost full view. The frontal keel may be 



1 Not always visible in all zooecia, unless suitably cleaned and mounted, and absent in the first-formed 

 zooecia of the colony, and in C. glabra MacGillivray which may be a synonym of C. darwinii, see p. 381. 

 Not shown in Busk's figures of C. darwinii (1884, pi. xxxii, fig. 6), but present in his specimens, see my 

 figures (Figs. 21 A, 22 A-C). 



