SPONGES. 177 



Acarnus, Gray. 



Ectvoninae in which the megascleres may be stylote, oxeote, tylote and cladotylote, 

 the latter forming the characteristic " grapnel-spicules " which typically echinate 

 the skeleton fibre. Microscleres may be present in the form of palmate isochelae 

 and toxa. 



Acarnus ternatus. Ridley. Plate VIIL, fig. 4. 



There is in the collection a remarkably fine rlry specimen of this species (R.N. 105, 

 Plate VIIL, fig. 4), of proliferous and thickly flabellate habit, with rather large vents 

 (about 8 millims. in diameter) on the summits of the lobes. The specimen measures 

 270 millims. in greatest breadth by 150 millims. in height, and its colour is brown. 

 There are also a couple of small specimens in spirit, the best of which is sub-cylindrical 

 in form and irregularly branched. 



The spongin of the skeleton fibres is very strongly developed but very pale- 

 coloured. 



Spicules. -(1.) Styli, measuring about 0"3 milbm. by 0"0164 millim. 



(2.) Cladotylota (grapnels), with usually three large, strongly recurved, sharp 

 teeth ; shaft about 0'21 millim. by 0"012 millim. 



(3.) Slender tylota with slightly spined heads ; about 0"22 millim. by 0"0035 millim. 

 in the middle. 



(4.1 Oxea ; long and very slender, gradually sharp-pointed at each end, may be 

 angulated at or near the middle ; say about 074 millim. hy 0"004 millim. 



(5.) Toxa; say about 0"152 millim. by 0*008 millim., but often more slender. 



(6.) Palmate isochelse, about 0'02 millim. long. 



The slender oxea occur irregularly distributed outside the horny fibres. Ridley (16) 

 makes no mention of them in his description, but they might be overlooked or 

 regarded as accidental. Keller, on the other hand, describes and figures similar 

 spicules in his Acarnus wolffgangi from the Red Sea (61). The latter species may 

 possibly prove to be a mere synonym of A. ternatus. 



The species has hitherto been recorded from Torres Straits (Ridley), Bombay (?) 

 (Ridley), Amirante Islands (Ridley), and Tahiti (" Challenger"). 



R.N. 105 (dry, Gulf of Manaar) ; 313; 329 (Ceylon seas). 



Cyamon, Gray (emend.). 



Ectyoninee in which the principal megascleres are smooth styli and tylostyli ; the 



echinating spicules have a radiate form, and there are no microscleres. 



In 1867, Gray (31) proposed this genus for Bowerbank's Dictyocylindrus vickersii, 



of which a single spicule was figured and described in the ' Monograph of British 



Spongiadee.'* It was not until 1879 that this species was first really described by 



* Vol. i., p, 267, fig. 23L 

 2 A 



