128 PROTOZOA. 



while their substance is composed of calcareous fibres ar- 

 ranged in a feather-like manner. Each pillar, further, is 

 attached to the centre of one of the plates of both the outer 

 and inner integuments, and the central tube of the pillar 

 opens into a system of horizontal canals which penetrate the 

 substance of these plates. In the plates of the outer integu- 

 ment there are four of these canals, springing from the main 

 tube of the pillar, directed towards the four angles of the 

 plate, defended by rib-like thickenings of the plate, and often 

 laid open by weathering (see fig. 29, B). In the plates of 

 the inner integument, on the other hand, the horizontal 

 canals are smaller, less clearly quadripartite, and more or 

 less ramified. 



As to its affinities, Mr Salter regarded Eeceptaculites as a 

 Foraminifer, and he placed it in the neighbourhood of Orbito- 

 lites. Mr Billings, however, pointed out that the genus has 

 some curious points of resemblance to the " gemmule " of the 

 fresh- water sponges, and he regarded it as being upon the whole 

 a sponge, having relationships with the Foraminifera. The 

 most recent researches upon the genus, by Giimbel, indicate 

 its proper position to be probably with the Foraminifera, 

 though it can hardly be placed in the immediate neighbour- 

 hood of any of the families of this order. The genus is 

 pre-eminently Silurian and Devonian, but Suess has indi- 

 cated its existence in rocks of Carboniferous age. It seems 

 likely that some problematical types, which have been doubt- 

 fully referred to the Sponges, to the Tunicates, or even to the 

 Cystideans, may really belong to the same family with Ee- 

 ceptaculites. This may be the ultimate destination of the 

 various singular bodies described by Billings as Pasceolus, by 

 Eichwald as Cydovrinus, by Salter as Nidulites, and by Pen- 

 gelly as Sphcerospongia, the true nature of all these being 

 still uncertain ; but the little that need be said about these 

 problematical forms will be given when treating of the Cys- 

 tideans. In any case, the Silurian genera described under 

 the names of Isckadites and Tetragonis are certainly the 

 same as Eeceptaculites. 



