58 DK. G. J. HINDE ON A NEW GENUS OF SILICEOUS SPONGES 



the interspace between the axis and the crust a layer with numerous 

 pin-like spicules, frequently in sheaf-like bundles with their pointed 

 ends directed to the exterior, and scattered globates as well. But 

 for the presence of this layer of skeletal pin-like spicules, of forms 

 characteristic of an important group of Monactinellid sponges, there 

 would have been considerable analogy between the present fossil 

 and Flacospongia. The possibility that pin-like spicules ma}'' have 

 been originally present in the interspaces between the anastomosing 

 wall-plates of this fossil sponge is not altogether excluded ; for 

 judging by their disposition in Flacospongia, they would be much 

 less likely to be preserved in situ than the dense axis of globates, 

 and some show of probability is given to this supposition by the 

 occurrence of a few detached pin-like spicules mingled with the 

 globates in the rock matrix. In the sponges themselves, however, 

 there is no evidence of an intermediate layer of pin-like or other 

 spicules ; their walls, as already stated, appear to be entirely com- 

 posed of the minute globates. As, moreover, we find that the globates 

 are associated in different sponges with various types of skeletal 

 spicules, Tetractinellid, Lithistid, and Monactinellid, there is 

 no antecedent improbability that they may exclusively form the 

 skeleton in this fossil. 



In addition to possessing a solid interior skeleton of globate 

 spicules, there is another point of resemblance between Placospongia 

 and this fossil, in the fact that the minute siliceous component 

 radial fibres of the globates in the two forms are very similar, 

 whilst they are distinctly smaller than the radial fibres of the 

 globates in Geoclia. 



The presence of a distinct zone of pin-shaped spicules in Flaco- 

 spongia and their apparent absence in this fossil indicates, how- 

 ever, a very marked systematic distinction between these forms : and 

 they may respectively prove to be types of two distinct families *. 



It may be inferred that the detached globate spicules probably 

 belong to more than a single genus and species, and it is therefore 

 necessary to propose a special designation for the particular sponge 

 above described. The generic name Renalina, given by Prof. 

 Elake to the globates, has moreover been preoccupied t. I propose 

 therefore to name this fossil genus Rhaxella %, and the family 

 Khaxellidie, with the following diagnosis : — 



* There is considerable difference of opinion as to tlie proper systematic 

 position of Placospovgia. By Dr. Gray and others it has been placed near 

 Geodia on account of the similarity of the globate spicules, whilst Mr. H. J.Carter, 

 F.Ei.S., relying on the characteristic pin-like spicules, places the genus in the 

 Suberitida, that is, with Monactinellid sponges (Ann. & Mag. Nat. Hist. ser. 5, 

 vol. vi. (1880), p. 477). Dr. Vosmaer states (Bronn's Klassen u. Ordn. des 

 Thierreichs, Spongien, p. 405) that it should probably come at the end of the 

 Geodidae. 



t See Lamarck, Hist. Nat. Anim. s. Vert. vii. p. 605(1822); Blainville, Diet. 

 Sci. Nat. tome xxxii. (1824). 



\ pd^, a berry, dimin. 



