398 COLLECTIONS FROM. MELANESIA. 



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

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

 observed here the cylindrical form of spicule wbich accompanies the 

 acerate in 0. armigera ; tbe vents are more abundant and the growth 

 is repent, instead of suberect. 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 decumbent and scarcely at all aculeated, shows how little 

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

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

 tion) is somewhat wide. 



26. Cladochalina pergamentacea. 



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

 p. 112, pi. x. fig. 4. 



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

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

 and spicules measuring - 09 by •001(5 millim. and shaped like those 

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



Hah. Thursday Island, Torres Straits, 3-4 fms. (on Retepora). 



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



ACERVOCHALINA, g. n. 



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



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 Chalina Umbata, Bowerbank (Mou. Brit. Spong. ii. p. 373 ; 

 ? Montagu). 



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

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

 and its serial vents. Mr. Carter 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 shoidd 

 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 Chalinidse. 



Schmidt has on reconsideration (Atl. Geb. p. 33) referred Chalina 

 Umbata to Chalinula ; but that geuus is equivalent to Chalina, 



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

 external form. viz. knife4ike shape, two marginal rows of vents, and smooth 

 surface, to differ specifically from C. armigera, and may therefore stand as 

 Cladochalina pert/a me nfacea. 



