170 BRITISH PALAEOZOIC SPONGES. 



surface is usually covered by numerous tubercles or blunt spines, which also 

 extend over the proximal upper portion of the rays ; in some cases the summit is 

 smooth, whilst the under or inner surface of the disc and rays is always smooth 

 and even. The transverse rays are compressed and sub-equal, they gradually taper 

 to a blunted extremity. The transverse rays of the dermal spicules are partially 

 fused together. There is considerable variation in the dimensions of the spicules. 

 A fairly large example is 4*3 mm. in width across the summit, and the individual 

 rays are about 2 mm in length, and about '7 mm. in width at the base. A small 

 spicule, on the other hand, is only 1*5 mm. across the summit, and the separate 

 rays are '7 mm. in length by *15 mm. in thickness. The average number of the 

 transverse rays is seven. 



This species differs from T. gracilis in the greater development of the central 

 disc, the distinct conical form, and more robust character of the transverse rays 

 of the spicules. These features are shown alike in the fragments of the dermal 

 layer and in the detached spicules. 



Distribution. — Carboniferous : Upper part of Lower-Limestone series, Law, 

 Low Baidland ; Thirdpart, Glencart, Waterlancl, Dairy. Lower part of Upper 

 Limestone series, Monkcastle Glen, Kilwinning, Ayrshire. (J. Young, J. Smith, 

 J. Bennie.) 



Also in bed of dark, pyritous shale in the Carboniferous Limestone of Ratingen, 

 near Dusseldorf. (Steinmanu.) 



46. Tholiasteeella geacilis, Hinde, sp. nov. Plate VII, figs. 1, 1 a — 1 g. 



The spicules of this species possess an elongate shaft, a central disc of moderate 

 dimensions, and from six to eight transverse rays. These are straight or curved, 

 circular or elliptical in section, and they gradually taper to an obtuse point. The 

 upper surface of the central disc is furnished with prominent blunted spines, and 

 in the spicules of the dermal layer there are obliquely-directed spines which form 

 notches, into which the rays of adjoining spicules are closely fitted. In some 

 instances also the rays are notched or furcated at their extremities (PI. VII, fig. 1 b). 



The dermal layer, as in the preceding species, is formed by the partial fusion 

 and interlacing of large and small spicules. 



In a large spicule the entire breadth of the summit is 5 mm., and the rays at 

 the base are *4 mm. in thickness. The breadth of a small spicule is 1*8 mm., and 

 the rays are - 2 mm. in thickness. The average number of the transverse rays 

 is six. 



This species is mainly distinguished from T. Yoimgi by the more elongated 



