116 ON CGELENTERATA FROM ZANZIBAR. [ Feb. 3, 
The arrangement of the canals and the general histology does not 
appear to differ materially from the description given by the same 
author ; but as the state of preservation of the Zanzibar specimens 
was not perfect, a detailed and critical examination of the sections 
was not made. I was fortunate enough to find, however, a few 
nematocysts that were exploded but remained in situ. They are 
(Pl. XIII. fig. 4) very similar in form to the small nematocysts 
of Millepora, and exhibit a vesicle and neck 0:01 mm. in length, 
armed with four barbs or spines. The thread was invariably 
broken, and I have no means of measuring its extreme length. 
The endoderm of the tentacles is solid. . 
The diagnosis of the species is as follows :— 
‘CERATELLA MINIMA, Sp. nov. 
Colony probably erect, branching strictly in one plane, irregularly 
and not very profusely. The main stems and all the branches 
cylindrical in form. Hydrophores very slightly developed. 
Skeleton consisting of dark brown longitudinally disposed horny 
fibres, united by loops and bands, forming in the larger branches 
a dense and firm but flexible skeletal plexus. 
Zooids situated slightly to one side of the plane of branching of 
the colony, alternately or in pairs, at distances of about 1 mm. on 
the terminal branches. Largest colony 29 mm. in height, with a 
maximum expanse of 65 mm. 
Locality. Ganzibar, shallow water. 
LITERATURE. 
1. J. HE. Gray.—Notes on the Ceratellade, a Family of Keratose 
Sponges. Proc. Zool. Soc. 1868, p. 575. 
2. H. J. Carrer.—Transformation of an entire Shell into 
Chitinous Structure by the Polype Hydractinia, with short 
descriptions of the Polypidoms of five other species. Ann. 
& Mag. Nat. Hist. ser. 4, 1873, x1. p. 1. 
3. W. M. Bate.—Some new and rare Hydroida in the Australian 
Museum. Proc. Linn. Soc. N.S. Wales, 1889, p. 748. 
4. W. B. Spencer.—On the Structure of Ceratella fusca. Trans, 
Royal Soc. of Victoria, 1892, p. 8. 
EXPLANATION OF PLATE XIII. 
Fig. 1. Drawing of the whole colony of Ceratella minima (specimen A) twice the 
natural size. The base of attachment is covered by an encrusting polyzoon. 
Vig. 2. A portion of a large branch and smaller branchiet taken from the region 
marked * in fig. 1, more highly magnified, showing the polyps P partially 
extended, bearing aa irregular number of knobbed tentacles, ¢.¢. At .h. are 
seen the rudimentary hydrophores. The figures show the general arrangement 
of the fibres of the horny skeleton. In the large branch they are closely 
crowded together. In the smaller branches the principal fibres are separated 
by considerable spaces but maintain a parallel arrangement. 
Fig. 8. A still smaller branch more highly magnified, in which there is only one 
primary longitudinal fibre. 
Vig. 4. One of the nematocysts of the tentacles. The diameter of the cyst is about 
0°01 mm. 
