398 OOLLECIIONS FKOM llELANEBIA, 



here few in number and reduced in dimensions ; the primary fibres 

 are more slender and much more strongly spicular, and I have not 

 observed here the cylindrical form of spicule which accompanies the 

 acerate in C. armigera ; the vents are more abundant and the growth 

 is repent, instead of subereot. Still I believe the species to be not 

 remotely allied ; and this near relation between two species, one of 

 which has an aculeated surface and an erect growth, while the 

 other is deoum|)ent and scarcely at all aculeated, shows how little 

 value for the group-distinction of the Chalinidee such characters may 

 possess. The variation shown by different specimens (see descrip- 

 tion) is somewhat wide. 



26. Cladoqhaliiia pergamentacea. 



Oladochalina armigera, var. pergamentacea *, Ridley, P. Z. S. 1881, 

 p. 112, pi. X. fig. 4. 



A young specimen of compressed form, smoott surface, and with 

 a row of vents along each margin, with the fibre as in C. armigera, 

 and spicules measuring -09 by -0016 millim. and shaped like those 

 of 0. armigera, seems to belong to the above form. 



Sfab. Thursday Island, Torres Straits, 3-4 fms. (on Setepora). 



Distribution. Hotspur Bank, off S.E. Brazil (Ridley). 



ACEEVOCHALINA, g. n. 

 Chalina, Schmidt, Suppl. ii. Adr. Meer. p. 10 (nee BowerbanK). 



Massive, sessile Chalinidse. Fibre strongly ceratinous, containing 

 axially or diffusely arranged slender acerate spicules, which do not 

 exceed in bulk the horny material of the fibre which contains them. 

 Vents distinct, ranged along upper surface. 



Type Ohalina limbata, Bowerbank (Mon. Brit. Spong. ii. p. 373 ; 

 ? Montagu). 



This genus appears to be most closely allied to Oladochalina, by 

 its strong relative development of keratose, its fine acerate spicules, 

 and its serial vents. Mr. Carler indicated the distinctness of such 

 forms as long ago as 1875, when (Ann. & Mag. N. H. (4) xvi. pp. 142, 

 162) he established the family Acervochalinida, making his first 

 group of the family Solida, in which Acervochalina would come. 

 He himself suggested the name which I have adopted, and has 

 sent me a specimen illustrating his view of the species which should 

 be assigned to the genus. The constancy in form of both this and 

 the following species, and their agreement in other points, show them 

 to be no mere dwarfed forms of erect Chalinidae. 



Schmidt has on reconsideration (Atl. Geb. p. 38) referred Ohalina 

 limbata to Chalinula; but that genus is equivalent to Ohalina, 



* This Bo-called variety seems, by the constancy of the peculiarities of its 

 external form, Tiz. knife-like shape, two marginal rows of vents, and smooth 

 surface, to differ specifioally from C. armigera, and may therefore stand aa 

 Cladochalma pergamewtacea. ' 



