New Species of Sponges. 



61 



account those produced on the original structures of these 

 sponges by what ma;y be termed the mechanical influences 

 of fossilization. Thei-e can be no doubt that they were 

 hollov; sacci-form or vasi-foim structures with veiy delicate 

 walls of spicular tissue, supporting the soft animal mem- 

 branes. They existed at the surface of the soft ooze of the 

 sea-bottom, probably their basal portions were embedded in 

 it, and they were furnished with elongated spicules whose 

 extension into the mud served to anchor them in one spot. 

 After the death of the animal, and t).e decay of the soft 

 tissues, the delicate skeletal framework would be gradually 

 buried in the accumulating sediments, until by their weight 

 it became completely flattened. Under favorable circum- 

 stances, the outline of the sponge and the natural arrange- 

 ment of the spicular skeleton would be preserved, and this 

 is fo. tunately the case with the specimens of Cyathophycus 

 from the Utica shale, and to a partial extent with one of 

 the specimens of Protospongia tetranema. More frequently, 

 however, probably owing to currents and other causes 

 acting at the surface ef the ooze, the skeletal framework is 

 partially or wholly broken up, so that only small patches 

 of the connected skeleton, oi- merely the dislocated and de- 

 tached spicules irregularly scattered over the rock sui'face 

 remain for determination, and this is the present condition 

 of the majority of the specimens from the Quebec group. 

 For some reason, probably connected with the arenaceous 

 character of the rock in which they occur, the neaily allied 

 sponges belonging to the Devonian genus, Dictyophyton, 

 Hall, usually retain their outer forms complete — that is, 

 without being compressed — but most of these sponges ex- 

 hibit only internal casts of their spicular skeleton, so that 

 at present we know very little of their original structures. 

 As already mentioned, nearly all these Quebec sponges 

 belong to the suborder of the Hexactinellidie, in which the 

 fundamental type or elementary spicule of the skeleton 

 consists of six equal rays, radiating from a common centre 

 at right angles to each other, forming three equal axes. 

 But I his typical form is subject to great modifications 



