— 6i — 



of the genera Phymatella, Callopegma, Turonia and Siphonia 

 (Studien iib. foss. Spong. laf. VIII, IX). As regards Siphonia 

 also the spicular structure has been well illustrated by Professor 

 SoUas (Quart. Jour. Geo. Soc. 1877. I'l. XXVI). In existing 

 sponges a similar form of spicule also occurs in Discodermia, 

 Theonella and Kaliapsis. With such small differences in the 

 structure and form of the spicule, it would be very difficult 

 to determine, e\'en were these free spicules well preserved, how 

 many of these fossil genera ma)' be represented, and it is 

 hopeless to make an attempt to do this, when the spicules, 

 as in the present instance, have been partially destroyed. 



The surface spicules (PI. IV. figs. 31 — 34 which I regard 

 as belonging to the same sponges as the minute four armed 

 skeleton spicules, differ from those which I have placed under 

 Ragadinia, in the absence of a central laminated disc ; the 

 head of the spicule being formed by three horizontally 

 extended sinuous arms which are once, and occasionally twice, 

 bifurcated. There are two well marked varieties in these 

 surface spicules; one form (figs. 31, 32) has the branches very 

 regular and even in width, with an average diameter of the 

 head of 1,1 mm.; the other form is very small and slender 

 and the terminal ends of the branches are deeply laciniated; 

 the diameter of this form is only 0,517 mm. These surface 

 spicules are present in greater numbers and in better preser- 

 vation than the mesh spicules, but they are also of but little 

 value for determining the particular genus of sponges to 

 which they belonged. To the smaller form (fig. 34) corres- 

 pond the laciniated spicules which Mr. Carter has described 

 from the Haldon Green Sand under the name of Dactylocal- 

 y cites Mcaryi (An. Mag. N. H. Vol. 7, p. 123, PL VII, figs. 

 1,2). The larger form (figs. 31,32) is nearly double the size 

 of the similarly shaped spicule from the Upper Chalk of 

 Westphalia, figured by Prof Zittel. (Ueber Coelop. Taf VII, 

 figs. 29, 30). 



