170 BRITISH PALAOZOIC 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 1s seven. 
This species differs from 7’. 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, Waterland, Dalry. 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. (Steinmann.) 
46, THOLIASTERELLA GRACILIS, Hinde, sp. nov. Plate VII, figs. 1, 1 a—1 g. 
The spicules of this species possess an elongate shaft, a central dise 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 (Pl. VII, fig. 1b). 
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. Youngi by the more elongated 
