156 BRITISH PALEOZOIC SPONGES. 



or canals opening at the truncated summit. Smaller canals extend radially from 

 the surface towards the central axis. The skeleton is composed of relatively large, 

 irregularly branching, spicules of great variety of form. The spicular branches 

 are usually curved, simple, or bifurcated, and they either taper to an obtuse point 

 or possess a flattened or slightly hollow facet at the extremity. These spicules 

 are united either by the interlocking of the tapering branches, or by the close 

 adpression of their facetted extremities to the rays of adjoining spicules, so as to 

 form a somewhat coarse, open, irregular meshwork. The dermal layer consists of 

 slender trifid spicules with elongated shafts, and small, simple, or compound head- 

 rays. The shafts of these spicules are inserted in the mesh-apertures on the 

 surface of the Sponge, whilst their head-rays slightly project outwards. Rarely, 

 however, are the dermal spicules preserved in situ. 



This genus makes its first appearance in the Carboniferous Rocks of Ayrshire, 

 in which the characteristic skeletal spicules are found, but hitherto no entire 

 Sponge ; in the Lower and Upper Greensand and the Chalk the genus is abun- 

 dantly represented. 



38. Doryderma Dalryense, Hinde. Plate V, figs. 7, 7 a — 7 c. 



1883. Doetdeema Daletense (in part), Hinde. Cat. Foss. Sponges, p 210, 



pi. xxxviii, figs. 7, 7 a —7 d; 

 cet. excl. 



The detached skeletal-spicules included in this species are more or less curved 

 and irregularly branching, the branches are cylindrical in section and generally 

 possess an elongate, concave, terminal expansion ; in some examples the branches 

 taper to an obtuse point. A fairly average spicule is 1 mm. in length and *18 mm. 

 in thickness. 



These spicules are of rare occurrence in the same deposits in Ayrshire in which 

 the detached spicules of Hyalostelia and other genera are abundant. In my 

 original description of this species I included in it some smaller spicules from Ben 

 Bulben, Sligo, but on further study I believe them to be quite distinct. 



Distribution. — Carboniferous : Upper part of Lower Limestone series ; Law 

 Quarry, Dairy (J. Bennie). Upper Limestone series ; Monkcastle, Kilwinning, 

 Ayrshire (J. Smith). 



