166 BRITISH. PALAOZOIC SPONGES. 
so-called stellate spicules are all of small dimensions, they vary from ‘3 to °67 mm. 
in diameter. In some the primary six rays simply bifurcate, in others one or more 
of the primary rays give off at their bases three or even four secondary rays, and 
these may also subdivide. The smaller rays of these stellates seem to have all 
originally possessed a spiral coil in the same manner as the larger, though it is now 
scarcely perceptible. 
These various forms of spicules were met with quite detached from each other in 
a bed of decayed chert, but there can hardly remain a doubt that they belonged to 
the same species. The spicules are now of chalcedonic and crystalline silica, they 
are of a creamy-white tint by reflected light, and translucent when examined in 
Canada balsam. Only rarely can the axial canals be detected. I am indebted to 
Mr. H. J. Carter, F.R.S., and to Mr. J. Wright, F.G.S., for the opportunity of 
studying the type-specimens. 
Distribution.—Carboniferous Limestone: Upper series, Ben Bulben, near 
Sligo, Ireland. 
Genus.—ACANTHACTINELLA,' Hinde, gen. nov. 
Syn.—Holasterella (in part), Hinde. 
Form of Sponge unknown; the skeleton consists of relatively large spicules of 
very varied and aberrant forms, but apparently modifications of the hexactinellid 
type. In thesimplest form there are only four rays in one plane at right angles to 
each other, in others, five rays are present, whilst other forms possess six rays. 
The rays may be straight or curved, sub-cylindrical or compressed. They fre- 
quently bifurcate near their ends, and give off irregularly, spinous processes, so 
that the extreme varieties are altogether abnormal in appearance. The spicules 
frequently exhibit wide canals; they are now of granular silica of a brownish tint. 
The spicules for which I propose this genus, differ very considerably in form 
and structure from any other detached Sponge-remains mingled in the same 
deposits with them. 
In many of them the number and arrangement of the rays appear to be in- 
definite, and they do not exhibit any regular plan of structure. In others, however, 
the primary rays are disposed like those of normal hexactinellid spicules ; but, owing 
to the irregular development of spines and the subdivision of the rays themselves, 
their typical character is largely masked. Further, their peculiar granular structure, 
and the large and often hollow interior canals, contrast very greatly with those of 
the other Sponge-spicules preserved with them under similar conditions, and seem 
1 dxavOa, a thorn; axriv, a ray, dimin. 
