HINDIA. v7 
1886. Catamopora FrBrosa, Steinmann. Neues Jahrb., Bd. i, Heft 1, p. 91. 
1886. Hinpra — Rauff. Sitzungsber. der niederrhein. Gesellsch. zu 
Bonn, p. i, sep. copy; also in Ann. and 
Mag. Nat. Hist., ser. 5, vol. xviii, p. 169. 
1886. — SPHHROIDALIS, Duncan. Ann. and Mag. Nat. Hist., ser. 5, vol. 
XViii, p. 226. 
1887. —_ riprosa, Hinde. Ann. and Mag. Nat. Hist., ser. 5, vol. xix, p. 67. 
1887. — SPH DROIDALIS, Duncan. Ann. and Mag. Nat. Hist., ser. 5, 
vol. xix, p. 260. 
The Sponges vary in form from nearly perfect spheres to biconvex dises, the 
outer surface is usually smooth and even. They range from 13 to 45 mm. in 
diameter. 
In the centre of the Sponge is a small round space filled by irregular spicular 
tissue ; from the outer border of this the canals radiate to the surface. The canals 
vary from ‘18 to *45 mm. in width, the smaller irregularly intermingled with the 
larger ; their apertures are for the most part oval or elliptical. The wall between 
the canals consists of only a single layer of spicular tissue. 
In most, if not in all cases, four rays are developed in the spicules. The central 
node is compressed, somewhat triangular in form, and slightly curved rays are 
given off from each corner (Pl. IX, figs. 3 c, d, e). The concave surface of the 
rays is smooth and even, whilst the convex is dentate or covered with tubercles. 
Their terminations are frequently considerably expanded, transversely to the ray 
itself. The fourth ray projects upwards from the centre of the node. It is usually 
only a short stumpy process terminating in from two to four conical spurs. The 
spicules are so disposed in the skeleton that the fourth ray pomts to the surface of 
the Sponge, whilst each of the other three rays is closely apposed to the nodes and 
convex surfaces of as many different spicules. Hach spicule, therefore, supports 
on its upper surface three rays converging to it from adjoining spicules. The 
junction of these rays conceals to a large extent the shortened fourth ray, so 
that as a rule only its terminal spurs can be seen. The spicular rays are about 
‘16 mm. in length, and ‘05 mm. in thickness. No canals have been discovered in 
them. 
The union of the spicules forms a closely reticulated skeleton with generally 
elliptical apertures, about ‘12 mm. in width, which appear as so many perforations 
in the walls of the radial canals. 
The only example of this species from British strata is a small, irregularly- 
shaped, nodular fragment, discovered by Prof. H. Alleyne Nicholson, in limestones 
of Ordovician age at Girvan, Ayrshire. The specimen appears to be incomplete, 
so that its entire figure is uncertain, and the spicular structure has been so com- 
pletely replaced by crystalline calcite, that the individual form and the union of the 
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