366 DISCOVERY REPORTS 



accentuated by the presence of ovicells or large frontal avicularia. These structures 

 project more or less in all four figures, but by comparing the position of the aperture 

 this rather misleading feature is discounted. 



The vibracula consist of a calcareous chamber containing the muscles which move 

 the seta, a calcareous groove in which the seta rests, and, at one side, a small rootlet- 

 chamber. The groove extends beyond the vibracular chamber, and the species differ 

 both in the proportion of the chamber to the groove and in the proportion of the whole 

 vibraculum to the zooecium. In C. boryi (Fig. 19 A) the chamber is small, the groove 

 is small and inconspicuous (though it may be longer than in Harmer's figure), and the 

 whole structure is small in proportion to the zooecium, leaving considerable areas of the 

 basal zooecial wall uncovered, even when the rootlet is in position. In C. helicina 

 (Fig. 20 A), C. darwinii (Fig. 21 C) and C. rostrata the chamber is larger than in 

 C. boryi and the groove is much more developed, forming a larger proportion of the 

 whole structure. More of the basal surface is thus covered and a more pronounced keel 

 is formed. When the rootlets are present the appearance of a fairly close oblique striation 

 of the basal surface is produced. In C. zelandica the chamber forms a rather larger 

 proportion of the whole, and the vibracula lie more closely together (Fig. 20 B). In 

 C. angusta and C. transversa Harmer (1926, p. 363) the chamber is very long, with the 

 result that no distinction between the chamber and the extension of the groove beyond 

 it is noticeable in the outline of the vibraculum as a whole. The vibracula are larger, 

 and are in close contact throughout their length, covering very nearly the whole of the 

 basal surface of the branch (Fig. 25 D). 



As pointed out by Harmer a calcareous bridge is constantly present, crossing the 

 groove near the articulation of the seta. From here nearly to the end of the vibracular 

 chamber the floor of the groove is membranous, so that the calcareous end-wall of the 

 chamber may form another bridge-like structure crossing the groove, as shown in 

 C. boryi by Harmer. Where, as in C. angusta (Fig. 25 D) and C. transversa, the chamber 

 is long and tapering, this second bridge is not noticeable. In C. zelandica (Fig. 20 B), 

 on the other hand, the short chamber ends much more abruptly, and the appearance 

 of a second bridge may be very marked. 



Key to the species of Caberea in the collection 



All the species in this key are biserial. 



1. Calcareous bar 1 across orifice, with scutum fused to it ... ... ... ... ... 2 



No calcareous bar, scutum may be connected to process from opposite border of opesia ... 4 



2. Vibracular chambers small, distant from each other. Single frontal avicularia sometimes 



much enlarged. Marginal avicularia not enlarged ... 1. C. boryi 



Vibracular chambers 2 large, near together or touching, single very large frontal avicularia not 



present, some marginal avicularia may be moderately enlarged .. . ... ... ... 3 



3. Branches stout, flat frontally, frontal avicularia small, proximal lobe of scutum often 



reduced 3. C. zelandica 



Branches not particularly stout, keeled frontally, 1 many frontal avicularia may be moderately 



enlarged, proximal lobe of scutum not reduced ... ... ... ... 2. C. helicina 



1 See p. 365. 2 See p. 366. 



