598 COLLECTIONS FROM THE WESTERN INDIAN OCEAN. 



Bowerbank, but differing in its very dense and opaque dermis, and 

 the strictly Dysidean distribution of its foreign bodies, viz. only in 

 the skeleton-fibres. The primary fibres are either single or multiple 

 in the same conulus, and range from about *07 to "36 millim. in 

 diameter. The sponge forms low, longitudinally-extended masses, 

 about 50 millim. (2 inches) in greatest length, 12 millim. in greatest 

 vertical thickness, throwing out rounded lobes which are 15 millim. 

 in greatest diameter. Vents round, few, placed near ends of lobes, 

 1 to 2*5 millim. in diameter. Texture in spirit rather elastic, com- 

 pressible. Conuli sharp-pointed, usually connected by radiating 

 ridges with each other; height "75 to 1 millim., distance apart 1-2 

 millim. Dermal membrane very dark grey, glabrous. Primary 

 fibres, as such, apparently existing only in the conuli, and not ex- 

 tending beneath them into the mass of the sponge ; secondary fibres 

 also very slightly developed, except in the ridges connecting the 

 conuli, where they form a dense network of horizontal fibres, ex- 

 tending to a depth of about 1 millim. below the surface. Skeleton- 

 fibres -05 to -18 millim. thick ; generally compact in structure, 

 exhibiting no horny substance to view. 



Hob. Mozambique, between tide-marks (on back of crab) ; Provi- 

 dence Island, Mascarene group, 19 fms. (on rock). 



Carter's species B. JcirJci, from Mauritius, South Australia, and 

 the Cape of Good Hope, above cited, may possibly include this ; but 

 as from his description and specimens it is evident that he groups 

 more than one species together, and as the present form is decidedly 

 distinct from Bowerbank's D. Tcirli (from the far smaller diameter 

 of the largest skeleton-fibres), it is not necessary to pursue the 

 question further. The very tough and opaque dermal layer and the 

 remarkable development of the secondary or horizontal fibre-system, 

 which assists in producing it, distinguish this Dysidea from all 

 intelligibly described species. Spongelia elegans, Nardo, as described 

 by F. E. Schulze, appears to approach it in the fasciculated arrange- 

 ment of the primary fibres, the proportions of the conuli, and the 

 general shape, but differs in its pale colour and in having the secon- 

 dary fibres more or less free from sand. 



0LIG0CERAS. 



Schulze, Zeitsch. wiss. Zool. xxxiii, p. 34. 



This genus, introduced (and rightly, as it seems to me) by Mar- 

 shall into this family, is based on a species from the Adriatic, 

 remarkable for a habit of attaching to itself foreign bodies of some 

 size. Prof. Schidze has expressed to me verbally a doubt as to 

 whether the genus will prove to have been rightly established. If, 

 however, this is due to the supposition that Oligoceras is a young 

 stage of a horny sponge, I think it may be set aside* by a consi- 



* Sinco writing the above, I have been assured by Dr. Polejaeff, whose Report 

 on the ' Challenger ' Ceratosa is in the press, that he has found the skeleton of 



