St>ONGES. 145 



and from the Mergui Archipelago (CARTER, DKNDY), as well as from the Gulf of 

 Mariaar (DENDY). 



R.N. 42 (Stat. LXI., Gulf of Manaar) ; 238 ? (deep water off Galle ; fragments). 



Petrosia similis, RIDLEY and DENDY. 



1887, Petrosia similis, RIDLEY and DENDY (1). 



There are in the collection a number of irregular, massive or more or less lol>ate 

 specimens, with numerous rather large, scattered vents, which I refer to this species. 

 The spicules measure about 0'22 millim. by 0'014 millim. The character of their ends 

 varies greatly, from strongylote to apiculate and sharp-pointed. 



The species was originally obtained by the " Challenger " from south of the Cape of 

 Good Hope and between Kerguelen and Heard Islands. 



R.N. 12, 61 (both from Gulf of Manaar) ; 289; 327 (Ceylon seas). 



Petrosia similis, var. delicatula, nov. 



This variety is distinguished from the typical form of the species by its more 

 delicate texture and smaller vents, which are usually more or less blocked up by a 

 strong development of gelatinous tissue. The spiculation differs little, if at all, from 

 that of the types. 



R.N. 84, 133, 276 (all from deep water off Galle and onwards up West Coast). 



Petrosia similis, var. halichondrioides, nov. 



In external appeara7ice this variety closely resembles P. nimilig, var. delicfitula. 

 The single specimen is strongly compressed, with the rather small but conspicuous and 

 widely open vents placed on prominent ridges. The texture (in spirit) is firm and 

 compact, but brittle. The skeleton is very confused and dense, without distinct 

 fibres, and the spicules are much more slender and Halichondria-]ike than in the 

 typical form, being gently curved oxea, for the most part gradually sharp-pointed at 

 each end, and measuring, say, about 0*2 millim. by 0'006 millim. 



R.N. 79 (Gulf of Manaar). 



Petrosia densissima, n. sp. Plate IX., fig. 9. 



Sponge massive, sub-conical, attached by the broad base ; with rather irregular surface 

 bearing feebly developed, meandering grooves. Surface minutely granular, without 

 distinct dermal membrane, slightly sandy. Vents very small and scattered Colour 

 (in spirit) rather dark greyish-brown on the surface ; pale yellowish-grey internally. 

 Texture extremely compact and hard ; stony ; incompressible. The larger of the two 

 specimens (R.N. 138A) measures about 40 millims. in height by 42 millims. in greatest 

 breadth. 



The skeleton is extraordinarily dense and compact, consisting of a sub-rectangular- 

 meshed reticulation of very stout spicular fibres, in which both primary and secondary 

 fibres are about as thick as the width of the meshes between them, say al>out 



u 



