ACAJ^THOEAPHIS.— CLTONA. 21 



dimensions ; a fairly large spicule measures 2-25 mm. in length by 0"975 mm. in 

 width. The spicules are now composed of iron peroxide. 



I am unable to determine whether this delicate film of large spinous spicules con- 

 stituted the entire skeleton of the sponge, or whether it formed merely the exterior 

 layer of a sponge whose interior skeleton has disappeared. Sufficient remains to 

 show that the form is entirely distinct from any hitherto known. The only specimen 

 is imbedded in soft chalk ; it formed part of the Bowerbank collection. 



Distribution. Upper Chalk : Shortlands, Kent. 



Genus SPONGILLA, Lam., 1816. 



Spongilla purbeckensis, Young. (Plate I. fig. 9.) 

 1878. Sjjongilla purbeckensis, Young, Geological Magazine, n. s. vol. v. p. 220, figs, a, b. 



The spicules of this sponge occur in great numbers in nodules or masses of chert ; 

 they are slightly curved acerates, fusiform, thickest in the centre, and gradually 

 diminishing to the extremities. According to Mr. Young the spicules are minutely 

 tuberculated ; but this feature is not shown in those which have come under my 

 notice. They vary from 0-015 to 0-0255 mm. in width; the longest measured is 

 0*45 mm. 



Some fragments of chert are principally composed of these spicules, which are 

 mingled together without any apparent arrangement. The specimen in the Museum 

 was presented by Mr. Young. 



Distribution. In freshwater limestones of the Purbeck series : Stare Cove, Dorset. 



Genus CLIONA, Grmit, 1826. 



Cliona ceetacea, Portlock, sp. 



IS^S. Entobia cretacea, Portlock, Geological Report, p. 360. 



1808. Parkinson, Organic Remains, t. 8. f. 10. 



1851. Clionites Conybeari, Morris, Ann. & Mag. Nat. Hist. vol. viii. p. 89, t. 4. f. 8, 9, 10. 



The examples of this species now occur as solid, spheroidal, ovate, or depressed 

 elongate siliceous bodies from 1*8 to 5-5 mm. in diameter, which are connected 

 together by numerous stolons into small groups. These bodies are usually found in 

 flints, partially filling the cavities formerly occupied by Belemnites, the tests of 

 Echinoderms, and the shells of Inoceramus. The original cavities hollowed out by 

 the boring sponge in these organic bodies have first been filled with silica, so as to 

 form solid moulds of that material ; and at a later stage the calcareous material of 

 the shells and tests has been dissolved away, leaving the siliceous infiUings intact. 

 These vary considerably in size, and also in their distance from each other ; but some 

 of the variations are probably owing ta the thickness and character of the shells and 



