230 PERCY SLADEN TRUST EXPEDITION 



The ectosome and the outer part of the choanosome contain numerous small, brown, 

 granular pigment-cells. I have not examined the canal system in detail, but it appears 

 to agree closely with that of Dercitopsis ceylonica [Dendy 1905]. 



Dercitopsis minor would appear to be a common species in the Indian Ocean. At 

 first I thought it must be specifically identical with the Ceylon form, but the fact that the 

 oxea never, in any of the specimens, seem to reach half the size that many of them attain 

 in D. ceylonica, renders it, in my opinion, desirable to recognise a specific distinction. 



The external appearance of the sponge strongly recalls that of a Chondrilla, with 

 which genus it may readily be confounded until examined microscopically, especially when, 

 as in the case of E.N. xxxiii. 1 a, the two are growing together. 



Register Nos., Localities, &c. xxxiii. 1 a, xxxiii. 2, and XLili. 3, Cargados Carajos, 

 30.8.05, B. 13, 30 fathoms; xlii. 6, Cargados Carajos, 30.8.05, B. 9, 30 fathoms; cii. 2a 

 (encrusting Erylus lendenfeldi), Amirante, 18.10.05, E. 25, 44 — 20 fathomg ; cxi. 7 and 

 cxiii. 12, Egmont Beef 



Sub-order 2. Astrotetraxonida Hentschel [1909]. 



Tetraxonida with astrose microscleres (except when these have been lost secondarily) ; 

 without sigmata or their derivatives. 



Family Pachastrellidse. 



Astrotetraxonida with calthrops and (or) short-shafted trisenes, usually scattered 

 irregularly in the interior of the sponge, though some of the short-shafted trieenes may be 

 definitely orientated, with the cladi supporting the ectosome. Without typical long- 

 shafted trisenes and without sterrasters. 



■ As already stated, this family is only retained provisionally. It is probably of poly- 

 phyletic origin, containing both primitive forms and degenerate stellettids. 



Genus Pachastrella Schmidt [1868]. 



Pachastrellidee with oxea and calthrops and (or) short-shafted trisenes for megascleres ; 

 without mesotriasnes ; with microrhabds and various forms of streptaster for microscleres, 

 but without spherasters. 



I must agree with Lendenfeld [1903] in merging SoUas's genus Poecillastra, which 

 I was at first strongly disposed to retain, in Pachastrella. There appears to be really 

 nothing but the plate-like form and the distribution of pores and oscula to distinguish the 

 two, and these characters vary so much that they cannot, at any rate in this case, be 

 regarded as of generic import. 



2. Pachastrella tenuilaminaris (Sollas). 



(Plate 45, fig. 2.) 

 Normania tenuilaminaris Sollas [1886]. 

 Poecillastra tenuilaminaris Sollas [1888]. 



Pachastrella crassiuscula Lendenfeld [1903]. ' 



Pachastrella tenuilaminaris Lebwohl [1914]. 



