HYALOSTELIA. 159 



proximal ray of the vertical axis penetrated into the interior of the Sponge (PL VI, 

 fig. 1). 



The spicules of the body of the Sponge are regular and modified hexactinellids. 

 In the simplest form, the rays are straight and gradually taper from the central 

 node to an obtuse point; the vertical axis is also considerably longer than the 

 transverse axes of the spicule. In other spicules the rays are very unequally 

 developed, and sometimes curved. In some, probably abnormal, forms, five of the 

 rays are reduced to small knobs. In other spicules the distal ray is not developed. 

 There are great variations in the dimensions of the skeletal- and dermal-spicules. 

 In small examples the principal axis is *64 mm. in length by *1 mm. in thickness, 

 whilst the main axis in large forms attains to 9 mm. in length by *54 mm. in 

 thickness. 



The spicular rods belonging to the anchoring appendage of the Sponge, occur 

 either in detached fragments, or as broad compressed bands, in which the 

 component rods are parallel to, and in contact with, each other. The rods are 

 smooth, cylindrical, and with a well-developed axial canal, and not infrequently 

 show traces of the concentric layers of which they are composed. In some, if not 

 in all cases, the rods terminate in four short, blunted, more or less recurved rays 

 (PL VI, figs. 2 e — 2 /c). No complete bundle of rods has been discovered; Messrs. 

 Youug have traced them to a length of 300 mm. (12 inches). The longest fragment 

 which has come under my notice has a length of 170 mm. by 38 mm. in width, and 

 from 5 to 10 mm. in thickness. There is also great variation in the size of the rods 

 in the same bundle; the majority vary from *95 to 1'35 mm. in diameter, but there 

 are smaller ones intermingled, which are not more than "15 mm. in thickness. 



The skeletal-spicules of this species occur for the most part independently 

 detached from each other, and mingled with spicules of other kinds of Sponges in 

 beds of decayed chert in the Lower Carboniferous strata of Scotland, Yorkshire, 

 North Wales, and Ireland. They also occur in close association with the ropes or 

 bundles of anchoring-spicules, but not infrequently these latter are met with in beds 

 which do not apparently contain the hexactinellid skeletal-spicules. This fact, 

 however, may be explained by the greater chance of preservation of the anchoring- 

 spicules owing to their penetration in the bottom ooze during the existence of the 

 Sponge. It may be assumed that the anchoring and the skeletal-spicules belong 

 to the same species. Further, the small fragments of the dermal layer of the Sponge 

 which have been met with afford a clue to the character of the skeletal-spicules of 

 the species, since they consist exclusively of simple and modified hexactinellids, and 

 thus justify excluding therefrom those peculiar forms which were originally supposed 

 to belong to this same species. 



The spicules of this species in the decayed cherts and limestones of the West of 

 Scotland are of a porcelain-white tint, the larger forms are opaque, but the smaller, 



