COLLECTED ON THE ' CHALLENGES ' EXPEDITION. 347 



circular mandible on one side of the base, and overhanging a wide 

 sinus ; on the older zocecia often a long, solid, upright acuminate . 

 spine, arising apparently from the side of the zocecium about the 

 middle of its length ; the rostrum often developed into a very 

 thick subcylindrical process, obliquely truncated at the end, and 

 presenting on the oblique face a large avicularium with a blunt 

 spatulate mandible and toothed beak (fig. *Jd). A few inter- 

 spersed immersed avicularia, usually placed transversely on the 

 front of a zocecium, and varying greatly in size ; the mandible 

 elongated, obtuse, or sub spatulate, with a simple rounded beak. 



Bab. St. 151. Off Heard Island, 75 fins., mud. 



As Prof. Smitt remarks, the typical 0. albirostris in a fresh 

 condition is readily recognizable by its greyish-brown colour and 

 blackish-brown opercula. The zocecia, he goes on to observe, in 

 the growing edge of the colony, are elongated ovate, presenting 

 the greatest resemblance to Cellepora bispinata, B. M. Cat. 



In this I quite agree with Prof. Smitt, and am strongly inclined 

 to think that his Cell, albirostris is identical with my C. bispinata. 

 Unfortunately I have no specimen of the latter to compare, and 

 the figure and description in the Brit. Mus. Cat. are hardly 

 sufficient to determine the point. Under these circumstances 

 I have thought it best to retain Prof. Smitt' s appellation. I 

 would remark, however, that my term of " very minute," as ap- 

 plied to the usual kind of rostral avicularium, quite accords with 

 that of C. albirostris. The large rostral avicularia are only 

 occasional. 



With respect to Prof. Smitt's supposition that C. albirostris 

 and my Cell, mamillata may be connected, if I understand him 

 correctly, I may observe that there can be no doubt of their 

 complete distinctness. Nor can I see any reason for regarding 

 the form described by Prof. Smitt, under the name of 0. (Dis- 

 copora) pusilla, as merely a variety of his C. albirostris. The two 

 seem to me to be quite distinct ; and how their close relation is 

 " incontestably proved by the very same form of their zooecial 

 aperture," seems to me to be by no means clear, seeing that the 

 form of aperture in question is one of very common occurrence. 



6. C. TBIDENTICTTLATA, n. sp.* 



Char. Zoarium lamellar, expanded, apparently unattached, 

 uneven. Zocecia deeply immersed; surface shining, granular, 



* " Chall. Eep." pi. xxix. fig. 3. 



