HINDU. 117 



1886. Calamopoea fibrosa, Steinmann. Neues Jahrb., Bd. i, Heft 1, p. 91. 



1886. Hindia — Banff. Sitzungsber. der niederrhein. Gesellsch. zu 



Bonn, p. i, sep. copy ; also in Ann. and 

 Mag. Nat. Hist., ser. 5, vol. xviii, p. 169. 



1886. — sphj3boidalis, Duncan. Ann. and Mag. Nat. Hist., ser. 5, vol. 



xviii, p. 226. 



1887. — FiBBosA, Hinde. Ann. and Mag. Nat. Hist., ser. 5, vol. xix, p. 67. 

 1887. — spHiEBOiDALis, Duncan. Ann. and Mag. Nat. Hist., ser. 5, 



vol. xix, p. 260. 



The Sponges vary in form from nearly perfect spheres to biconvex discs, 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 (PI. 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 points 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. Each 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, ana *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 Grirvan, 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 



Q 



