174 BRITISH PALAEOZOIC SPONGES. 



in thickness, whilst in a large one they reach a length of 3 mm. by '6 mm. in 

 thickness. 



In the complex corolla-like spicules the number of horizontal rays varies from 

 eighteen to thirty, they are in close contact, and apparently amalgamated laterally 

 for about half their length, and thus form a platter-shaped central depressed disc. 

 The upper surface of the ray is usually covered with minute conical tubercles, 

 which in some cases have the appearance of secondary rays. The corolla-like 

 summit of the spicule, which ranges from 1*6 to 4 mm. in breadth, is supported on 

 three to five stout conical rays, which appear to have extended into the interior of 

 the Sponge, whilst the expanded summits formed the surface-layer of the Sponge. 

 In addition to the larger spicules there are also small subspherical spicules, con- 

 sisting of numerous minute, obtusely-pointed, subequal rays, nearly in contact 

 with each other. 



The spicules are siliceous, and exhibit the same appearance as those of 

 Hyalostelia and other siliceous Sponges in the same deposits. In no case have I 

 been able to recognise axial canals in them. 



The spicules in these species are distinguished from those of A. tumida by the 

 more elongated character of the rays as well as by differences of form. 



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

 Blackstone, Waterland, Dairy, Ayrshire. (J. Smith, J. Bennie, J. Young.) 



50. Asteractinella tumida, Hinde, sp. nov. Plate IX, figs. 1, 1 a — 1 g. 



The simpler spicules of this species are star-like in form, consisting of from 

 five to nine subequal, relatively short, very stout simple conical rays, radiating from 

 a common centre. In the more complex forms, the longer rays are supplemented 

 by a group of small conical rays in the central portion of the spicule, which are 

 frequently subdivided at their summits. Spicules with vertical axes are also present 

 as well as corolla-like spicules of the same general form as in the preceding species, 

 but with more conical rays. The spicules included in this species vary considerably 

 in size. The star-like forms are from 2 to 3 "5 mm. in diameter, and the rays are 

 •85 mm. in thickness at their bases. In contrast with the larger forms, the smaller 

 spicules are only '45 mm. in extension, and the rays are not more than '1 mm. in 

 thickness. 



The spicules of this species are characterised by the conical robust form of their 

 rays. In fragmentary portions of the skeleton which have been found, the larger 

 and smaller spicules are intermingled, and their rays are partially fused together, 

 but the greater proportion of the spicules are now quite free from each other. 



