272 Report of the State Geologist. 



is constituted by a circle of eight or four plates. The apical pole 

 is closed by a variable, but always large, number of plates. 



4. Each of the B.vg arms of the skeletal elements or spicules 

 is traversed by an axial canal, the canals of the four tangential 

 arms having a conspicuously fusiform shape. 



5. The radial arms or pillars terminate on the inner or ' gas- 

 tral ' side in a conical dilation, which, is laterally extended till 

 adjoining pillars touch. This internal thickening of the radial 

 pillars is not furnished, with a special plate, corresponding with 

 the external plate, and is not penetrated by transverse canals. 



6. The inner or ' gastral ' wall of the fossil is imperforate, 

 the pores described by Billings being the result of fossilization. 



7. The genus Ischadites agrees essentially with Receptaculites 

 in structure, but its skeletal elements are more slender. An 

 apical aperture is in some cases clearly wanting in Ischadites, 

 and probably did not exist at all. 



8. The genus Acakthochonia is identical with Ischadites. 



9. The geological range of Ischadites extends to the Upper 

 Devonian. 



10. The genus Pultgonosph^ rites (Sph^rospongia) is simi- 

 larly constructed to Reckptaculites as regards the tangential 

 arms of the spicules, but the radial arms or pillars are wanting. 



11. The BeGeptaGuUtidcB are not silioeous organisms, but the 

 skeleton was originally calcareous, and the siliceous examples are 

 the result of silicification. ' The group, therefore, can not be 

 referred to the Hexactinellid sponges, and its systematic position 

 is still entirely uncertain." 



These conclusions, as given b}^ Raufp-, embody, in large measure, 

 the results obtained by previous writers on Receptaculites, and 

 furnish a basis for additional investigation. 



Upwards of twenty specimens, including fragments, of Recep- 

 taculites infundihuliformis have been examined by me, exemplify- 

 ing several different conditions of preservation. Qf these, one in 

 which the original tissue has been replaced by pyrite, is of unusual 

 interest. The excellence of pyrite as a medium of preservation 

 for fossils is shown in the recent discovery, in the Utica slate, of 

 Trilobites retaining antennae and other append iges. The speci- 

 men in question leaves little to be desired in the way of preserva- 

 tion. It displays details of structure rarely indicated, and may 

 serve to throw some light on the phylogenetic position of this 



