Mr. H. J. Carter on Spongilla cinerea. 263 



Mr. Hinde's conclusion that the Atlantic deep-sea mud is 

 filled (as he seems to think) with these spicular skeletons 

 except at its immediate surface. Hence the evidence furnished 

 by the Horstead flint proves rather that, were it not for the 

 special agency of the colloidal protoplasm and the conditions I 

 have elsewhere fully described, the Horstead Chalk, in common 

 with the rest of the Upper Chalk strata, must still have re- 

 tained within its substance the silica which, under the pre- 

 vailing conditions, entered into the formation of the stratified 

 flints. 



Mr. Hinde seems to have imagined that I disputed the con- 

 temporaneous existence of Sponges and Forarainifera. A 

 reperusal of my first paper on the subject, and a glance at 

 pp. 200-202 of my paper in the ' Annals' for Feb. 1881, 

 will, I think, satisfy him that, so far from this being the case, 

 the contemporaneous development of both these animal types 

 constitutes an essential element in my hypothesis of the flint 

 formation. 



XXV. — On Spongilla cinerea. 

 By H. J. Carter, F.R.S. &c. 



Having omitted to insert a description of Spongilla cinerea in 

 my compilation of the " History and Classification of the 

 known Species of Spongilla^'' in the last number of the 

 ' Annals,' p. 88, after S. cerebellata^ Bk., it is herewith 

 supplied. 



Spongilla cinerea^ Carter. 



Spongilla cinerea, Carter, No. 12, p. 82, pi. iii. fig. 5 ; No. 20, p. 30, 

 pi. xxxviii. fig. 19. 



Flat, spreading ; surface slightly convex, presenting gentle 

 eminences and depressions. Colour cinereous ; texture com- 

 pact, fine, friable. Skeleton-spicule curved, fusiform, gra- 

 dually sharp-pointed, minutely spined. Statoblast globular ; 

 aperture infundibular ; crust thick, white, composed of micro- 

 cell substance charged Avith minute acerate spicules, which 

 are curved, cylindrical, abruptly sharp-pointed, and coarsely 

 spined throughout, arranged more or less tangentially, inter- 

 crossing. 



Loc. Bombay. 



Ols. The chief characters of this species are its cinereous 

 colour and fine texture ; its elementary parts are the 

 smallest of any species that I have yet examined. 



