ASTERACTINELLA. 173 



partially fused together, but this probably arises from the fossilization ; the 

 numerous instances in which the spicules are now entirely free seem to indicate 

 that they were originally only held together by the soft structures of the Sponge. 



The character of these spicules clearly distinguishes them from the other 

 detached forms with which they are associated ; and the occurrence of fragments 

 of the Sponge-skeleton exclusively composed of them likewise shows that they are 

 distinct. No trace of any derivation from the hexactinellid type is perceptible in 

 any of these spicules ; even in the simplest form more than six rays are present, 

 and there is no indication that they may have originated from the subdivision of 

 the rays of a normal hexactinellid spicule. 



Some of the spicules included in this genus were referred by Mr. Carter to 

 Holasterella conferta, and relying on his definition I likewise relegated them to the 

 same species in the ' Cat. Foss. Sponges ;' but, as already mentioned, in a subsequent 

 examination of the type form I have been unable to discover any of these forms 

 in it. 



Two species of this genus have been recognised in the Carboniferous strata of 

 Ayrshire. 



49. Asteractinella expansa, Hinde, sp. nov. Plate VIII, figs. 3, 3 a — 3 h. 



1877. Hyalonema Shithii (in part), Young and Young. Ann. and Mag. Nat. 



Hist., ser. 4, vol. xx, pi. xiv, figs. 20, 21. 



1878. — — ? (in part), Carter. Ann. and Mag Nat. Hist., ser. 5, 



vol. i, p. 133, pi. ix, fig. 11. 



1879. Holasteeella confeeta (in part), Carter. Ann. and Mag. Nat. Hist., 



ser. 5, vol. iii, p. 141, pi. 



xxi, figs. 4, 5, 7, cet. excl. 



1883. — — Hinde. Cat. Foss. Sponges, p. 152, pi. xxxii, 



figs. 2-2/. 



In the simpler spicules there is a prominent vertical ray, from the summit of 

 which nine to twelve robust rays diverge at various angles ; a variable number of 

 small conical rays are also frequently present. In other spicules there is a distinct 

 vertical axis, whilst not infrequently no distinct vertical ray or axis is present, and 

 the spicule consists of seven to twelve rays of varying lengths in addition to 

 several subordinate conical rays, all radiating from a common centre. The rays 

 are straight or slightly curved, circular in transverse section, and they gradually 

 taper to an obtuse point. The smaller central rays are sometimes divided at their 

 tips. In a small spicule the principal rays are *65 mm. in length and *125 mm. 



