ACANTHACTINELLA. 167 



to point to fundamental differences in their nature. These peculiar features 

 suggested to Mr. J. Young that they might have been produced by an incrustation 

 over other Sponge-remains ; but since no other spicules yet found in these beds 

 present the same remarkable forms, it can hardly be assumed that they have 

 originated in this manner. 



These spicules appear to belong to a single species ; they have as yet only been 

 met with in the Carboniferous deposits of Ayrshire. 



44. Acanthactinella Benniei, Hinde. Plate VIII, figs. 4, 4 a — 4 i. 



1883. Holastebella Benniei, Hinde. Cat. Foss. Sponges, p. 153, pi. xxxii, 



figs. 5 — 5 e. 

 1877. Incrusting Sponge?, Young and Young. Ann. and Mag. Nat. Hist., 



vol. xx, p. 429, pi. xv, fig. 41. 



The characters of the species have been enumerated in the description of the 

 genus. Usually the rays bifurcate near their extremities, but not infrequently there 

 is a tripartite division. The rays terminate obtusely. As a rule the spicules are 

 entirely detached, but in one or two cases a fusion of the principal axes of two 

 spicules has taken place so that they now appear as one (PI. VIII, fig. 4 d). The 

 axes of the spicules vary from 2 - 5 to 4 mm. in length, and the rays are from *5 to 

 •9 mm. in thickness. 



In my original description, this form was placed in the genus Holasterella, but 

 its characters now seem to me to be at least generically distinct. 



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

 ningham Baidland, Low Baidland, Law, Dairy, Ayrshire. (J. Bennie, J. Smith, 

 J. Young.) 



Flesh-spicules of Hexactinellids. Plate IX, figs. 13, 13 a. 



In microscopic sections of the chert Sponge-beds of Yorkshire, I have recently 

 found two distinct forms of flesh-spicules, which I am at present unable to place 

 with any of the skeletal- spicules previously described. One form (fig. 13) is a 

 regular six-rayed spicule, the rays are sub-equal, tapering, and furnished with blunt 

 spines projecting at right angles from their surfaces. This spicule is '23 mm. in 

 its longest axis, and the rays are '02 mm. in thickness. It is present in the 

 Yoredale-beds at Richmond. 



The other spicule (fig. 13 a) is a six-rayed form, in which each of the principal 



