488 MR. A. W. WATERS ON 



The operculum is membranous, with a diagonal band or sclerite 

 on each side to which the muscle for closing the operculum is 

 attached ; but also attached to the same sclerite there is a muscular 

 band fastened to the tentacular sheath. I have not noticed a 

 double attachment like this before, but examination may show 

 that it occurs in other species. 



In a large proportion of zooecia thei'e are two polypides of 

 about the same size, so that 20-30 zooecia with two polypides 

 may be seen adjoining one another, whereas other pieces may 

 show a much more limited number of double polypides. Although 

 budding polypides in the same zorecia as mature polypides are 

 known to us all, and have been described by Haddon*, OstromofFt, 

 and HarmerJ, they are only in a limited number of zooecia ; nor 

 have I been able to see that they are the same as the two zooecia 

 described by Prouho § in Alcyonidium duplex P. The two tenta- 

 cular sheaths are side by side, and are attached to the operculum 

 and the neighbouring wall. No ovaiia or ova have been seen, 

 and only in a very few cases were testes found occurring in round 

 masses near the lateral wall. 



From the lateral walls there are bundles of muscles (6-12) 

 attached to the frontal membrane of the zooecia. 



In all the lateral walls there are pores at fairly regular 

 intei-vals all over the walls, and besides there are in some cases 

 disks with numerous pores near the opercular wall. Further, in 

 a bilaminate piece of M. armata, there are in several cases large 

 perforated disks on the basal walls, like those described in 

 Petralia for the radicle attachment, though, strangely, in the 

 unilaminate parts no distinct perforated disks have been found. 

 This form cannot remain under Membranij)ora^ though I am not 

 suggesting that it is Petralia, but call attention to various similar 

 characters in forms placed far asunder. 



There are about 30 tentacles, which is a larger number than 

 has been found in any true Memhranipora. Memhranipora nigraiis 

 Hincks and M. marginella H., with avicularia similarly placed 

 near the distal end, have also curious large vicai-ioiis avicularia. 



Loc. Port Denison, Holboi^n Island, 2<"» fath. { Jlastoell) ; Port 

 MoUe, Australia ; Sagamibai, Japan, 40 fath. (Ortniann). Wasin, 

 Brit. East Africa, 10 fath. (500) ; Zanzibar Channel, from under- 

 side of buoy (528), collected by Crossland. 



Membranipora catenularia Jameson. 



For synonyms see Miss Jelly's Catalogue. 



Although the Arctic M. monostachys Busk from Franz Josef 

 Land has many points of similarity, the operculum in M. catenu- 

 laria from Zanzibar is only about half the width of that of the 



* Quart. Journ. Micr. Sc. vol. xxiii. p. 520 (1883). 

 t Arch. Slaves de Biol. vol. ii. p. 341 (1886). 



X " Excretory Processes in Marine Polyz.oa," Quart. Journ. Micr. Sc. p. 139 (1891). 

 § "Cent, a riiist. des Bry.," Arch, de Zool. Exp^r. et Gen. 2nd ser. vol. x. p. 581 

 (1892). 



