16 THE VOYAGE OF H.M.S. CHALLENGER. 



Cellaria australis, MacGillivray (PI. II. figs. 1-4). 



Cellaria fisiulosa, var. australis, MacGillivray, Zool. of Vict., dec. v. p. 48. 

 Cellaria australis, MacGillivray, Trans. Roy. Soc. Vict., vol. xxi. p. 93. 

 Salicornaria clavaia, Busk, Zool. Chall. Exp., part xxx. p. 88, pi. xii. fig. 8. 

 Cellaria fistulosa, var. australis, Hincks, Ann. and Mag. Nat. Hist., ser. 5, vol. xiii. p. 368, 

 pi. xiv. fig. 4. 



This is a very distinctly marked species, with very characteristic opercula and 

 mandibles, well described by MacGillivray, but Busk seems to have been unaware of 

 his later and fuller descriptions, and only refers to the earlier one. 



This, being a larger species than most of the Cellaria, is more favourable for studying 

 in cross section, and some sections prepared Rewarded me by showing in the clearest 

 manner the function of what Mr. Busk calls the " foramina " of the operculum. These, 

 instead of being as Busk supposed conical projections, are hollow sockets into which the 

 denticles of the proximal edge of the aperture articulate. 



An operculum in transverse section is shown in fig. 2. What Busk calls the 

 granulated band is much thicker than the rest of the operculum, whereas the upper part 

 and the " foramina " are thin. 



Having worked out the signification of the lower denticles, I naturally asked, what are 

 we to understand by the upper denticles, which occur in a few species, as Cellaria rigida, 

 MacGillivray, &c., but I have not been able as distinctly to follow out the working of 

 these, though no doubt the " branched chitinous support " is connected with them. Thus 

 we have correlated structures, and, seeing that various fossils have these two pairs of 

 teeth, this is of considerable importance. In Cellaria rigida the proximal pair of teeth 

 are at a higher level than the distal (see fig. 5). The shape of the cover to the ovicell 

 would seem to be specifically important. From each zooecial chamber of the Cellaria a 

 long tube arises which expands into the chamber above, and from the middle of these 

 tubes there is a connection, of course, through a rosette plate to the zooecia on each side. 

 In one of the Challenger specimens the connecting chitinous tubes of a new branch follow 

 the lines of the border of the zooecia transversely across the zoarium forming zigzag lines. 



Cellaria rigida, MacGillivray (PI. II. figs. 5-7). 



Cellaria rigida, MacGillivray, Trans. Roy. Soc. Vict., vol. xxi. p. 92, pi. i. figs. 1, 2. ; Zool. of 



Vict., dec. xi. p. 17, pi, 105, fig. 1. 

 Salicornaria simplex. Busk, Zool. Chall. Exp., part xxx. p. 88, pi. xxxiii. fig. 8. 



I have already referred to the shape of the teeth and to the connection from cell to 

 cell when discussing the last species. 



