— 59 — 



diminishes in thickness and becomes divided into twig like 

 branches. 



The surface spicules which I regard as probably belonging 

 t(i this species vary in form from discs with a rudely indented 

 edge, to spicules with but a small central disc, from which radiate 

 bifurcate expanded arms. In nearly all the forms there are 

 indications of a shaft, but this is reduced to a very minute 

 point. No indications of canals are exhibited in these spicules 

 but in similarly shaped spicules from the Westphalian Chalk, 

 three small canals are shown radiating from the point of the 

 shaft, and this point is frequently not in the centre of the 

 disc. There are such numerous transitional forms between 

 the spicules with but a slightly indented disc, and those in 

 which there are three main arms with bifurcated extensions, 

 that it is impossible to separate these spicules into discoid 

 and branched forms, but, on the other hand, a distinction can 

 be made between the branched surface spicules with a central 

 disc which I place in Ragadinia, and the branched surface 

 spicules without a central disc and with much narrower arms, 

 which probably belong to the Genus Racodiscula. 



The sponges which serve as the t>'pe of the Genus 

 Ragadinia:, R. rimosa, Roem. sp., are platter-shaped bodies 

 with rounded edges and short base. The spicular arms of 

 the type species are very unequal in length and are ornamented 

 with warty prominences similar to those of the G. Plinthosella. 

 Professor Zittel , in his description of the genus, states that 

 there are very numerous specimens in the Upper Chalk of 

 Ahlten in Hanover which had all been referred to one species 

 R. rimosa, Roem. but could probably be divided into two or 

 three different species. On comparing the Horstead spicules 

 with mounted specimens of the spicules oi R. vimosa, in the 

 Palaeontological Museum at Munich I find that they differ in 

 having but a single ring-shaped expansion on the arms and 

 in the absence of the warty projections. There is however a 

 mounted specimen from Hanover, labelled R- rimosa, which 



