134- Revieivs — i)r. G. J. Binde\^ Fossil Sponges. 



" 7. Calcispongi^, Blainville. 



" Sponges with skeletons of calcareous spicules. 



" The first of these existing orders, the Myxospongics, is of course 

 quite unknown in the fossil state, and it is also very doubtful 

 wliether any remains of the next order, the Ceratospongice, have been 

 preserved. Certain casts of cylindrical bodies from the Cretaceous 

 system have been regarded as belonging to horny sponges ; but 

 in. the absence of all other characters but that of outward form, 

 tbese bodies cannot be definitely placed in this group. 



" The MonactineUidce have comparatively few representatives in 

 the fossil state, and they present a striking contrast to the abundance 

 of this order in the present seas. Their rarity as fossils, howevei', 

 is not to be accepted as an indication of their scanty existence in 

 the past, but is more probably owing to the fact that the spicular 

 structure of these sponges is unsuitable to their preservation as 

 fossils. 



"The structure of the Tetractinellidce, like that of the order just 

 mentioned, is also but little adapted to the retention of the form of 

 these sponges in the fossil state ; but the constituent spicules of many 

 of these sponges are relatively large and robust, so that they are 

 capable of preservation, and they are frequently met with detached 

 4nd scattered through the rocks. In some instances they are suffi- 

 ciently numerous to form thin beds, almost exclusively composed of 

 spicules. It is therefore probable that this order of sponges flourished 

 as abundantly in the seas of the Neocomian period as at the present day. 



" Lithistid and Hexactinellid sponges, unlike those of the previous 

 groups, are more numerous and varied in the fossil, than the recent 

 state. The spicular components of the skeleton in these sponges are 

 firmly attached together-; consequently the form of the sponge is 

 frequently preserved intact, even in cases where the spicules them- 

 selves have subsequently been destroyed. The occurrence of detached 

 spicules and fragments of the skeleton scattered through the rocks 

 plainly shows, however, that only under favourable conditions of 

 fossilization has the form of the sponges been retained, and those 

 now remaining probably comprise but a small proportion of the 

 number which previously existed. 



" Fossil calcareous sponges are abundant in certain strata, but they 

 belong to a family which differs to such an extent from existing 

 CnlcispongicB that the relationship has been greatlj' doubted. Eecent 

 discoveries, however, prove that the component spicules in the fossil 

 Calcispongice possess the closest resemblance to those of the living 

 examples of the order." 



The formations in which fossil sponges most commonly occur are 

 those with calcareous or arenaceous beds ; they are rarely met with 

 in shales or deposits formed fi'om muddy sediments. Cherty layers' 

 and nodules of flint frequently abound in fossil sponges. Both 

 arenaceous and calcareous deposits seem to have been favourable 

 to the preservation of Tetractinellid and Lithistid Sponges ; for they 

 occur alike in the Lower and Upper Greensands and in the Chalk. 



The Hexactinellid sponges on the other hand favour more par- 



