150 SILICEOUS SPONGES. 



surface numerous hexactinellid spicules apparently detached and irregularly mingled 

 together. Slender monactinellid spicules are also present. The specimen has been 

 treated with acid, and the spicules are now in the condition of iron peroxide. A 

 large spicule is 3 mm. in length. The interior structure of the specimen, owing to 

 its condition, cannot be determined ; but it is probably made up of spicules similar to 

 those on the exterior, and as these resemble the detached forms to which I have given 

 the name of S. cretacea, I refer this sponge to the same species. 



Distribution. Upper Chalk : Horstead, Norfolk ; South of England {coll. Bower- 

 lank). 



Family TOLLAXIDM, Marshall, 



Genus HYALOSTELIA, Zitt. 1878. 



Hyalostelia Smithii, Young and Young, sp. (Plate XXXII. figs. 1-1^.) 



1876. Acanthospongia Smithii, Young and Young, Cat. Western Scottish Fossils, p. 38. 



1877. Hijalonema Smithii, Young and Young, pars, Ann. & Mag. Nat. Hist. vol. xx. p. 426, 

 t. 14. f. 1-3, .'^-12, 14-17. 



1877. Acanthospongia Smithii, Zitt. Studien, I Ab. p. 60. 



1878. Hyalonema Smithii, Carter, pars, Ann. & Mag. Nat. Hist. vol. i. p. 129, t. 9. 

 f. 1-9, 12, 13. 



This species was constituted by Messrs. Young to include detached spicules of 

 various forms which occur, freely intermingled together, in beds of decayed chert of 

 Carboniferous age in Scotland. Many of these spicules are simple Hexactinellids, 

 that is with six rays at right angles to each other, whilst others have a greater 

 number of rays, though they appear to be but varieties of the Hexactinellid type. 

 Messrs. Young suggested the probability that these various forms of spicules might 

 belong to more than a single species of sponge ; and this was shown to be the 

 case by Mr. Carter, who subsequently described a sponge, Holasterella conferta, which 

 is composed of some of the abnormal hexactinellid spicules which Messrs. Young 

 had included in 11. Smithii. I therefore propose to restrict //. Smithii to the 

 simple hexactinellid spicules, which are the most abundant forms in the beds at 

 Cunningham Baidland, and to the spicular rods with or without the four anchoring- 

 hooks at their termination. The simple spicules usually have a main axis, which 

 varies from 1'5 to 9 mm. in length ; the other axes are generally very unequal, and 

 the rays are frequently inflated, and sometimes reduced to a mere rounded knob. The 

 spicular rods are met with singly or disposed parallel with each other in compressed 

 bundles; they are of indefinite length, and vary from '3 to 1"5 mm. in diameter. 

 When perfect they terminate in four short, recurved, anchor-like rays. These rods 

 are regarded by Messrs. Y^oung as identical with those described by M'Coy under the 



