diminishes in thickness and becomes divided into twig-like 
branches. 
The surface spicules which I regard as probably belonging 
to 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 surtace 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 type 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 of R. rzmosa, 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. rzmosa, which 
