138 BRITISH PALEOZOIC SPONGES. 



Genus. — Rbceptaoulites, Defrance. 

 1827. Dictionnaire des Sciences Naturelles, tome 45, Atlas, pi. 68. 



Syn. — Coscinopora (in part), Goldfuss, D. Dale Owen. 



Generic Characters. — Cup- or platter- shaped Sponges, growing from a small 

 inverted conical nucleus, and frequently reaching considerable dimensions. Wall 

 thick, the outer or under surface consisting of rhomboidal spicular plates similar 

 to those in Ischadites, and, as in this genus, disposed in decussating lines. The 

 four transverse or horizontal spicular rays form radial and concentric lines beneath 

 the surface-plates. The vertical or entering ray of the spicules is sub- 

 cylindrical, frequently constricted near its junction with the transverse rays ; at 

 its inner end it expands, to form a small horizontal plate, which is traversed by 

 horizontal canals. By the junction of the inner plates with each other a distinct 

 inner or upper layer of the Sponge-wall is formed, and in one species at least this 

 layer is perforated by cylindrical canals, thus giving communication to the interior 

 space of the Sponge-wall. 



This genus is distinguished from all others included in the family by the 

 presence of an inner layer formed by the development of small plates at the 

 extremity of the entering ray of the spicules. 



Owing in part to the peculiar aspect of examples of this genus under different 

 conditions of preservation, various views have been held as to its character and 

 affinities. By Defrance and Bichwald the hollow casts of the vertical spicular 

 rays were believed to be polyp-cells, and the genus was placed with Corals. 

 Salter at first regarded it as a Foraminifer allied to the family of the Orbitolitidse ; 

 Billings placed it with Sponges on account of a supposed resemblance to the 

 gemmules of Spongilla ; by Dames it was placed a second time with the Foramini- 

 fera as the type of a family near the Orbitolitidas ; and still later Giimbel retained 

 it in the same class, but included it in the family of the Dactyloporidse. 



The genus makes its first appearance in the Ordovician of North America, 

 Russia, and the Arctic regions ; it is present in the Silurian proper at Malvern ; 

 Australia, and doubtfully in Canada ; in the Devonian of Devonshire, Belgium, the 

 Eifel, and elsewhere in Germany as well as in Canada ; and a single somewhat 

 doubtful species is recorded from the Carboniferous Limestone of Silesia. 



