I 



RANGE OF FOSSIL SFONGES 73 



Nevertheless, isolated spicules prove the existence of Monactinellids and 

 Tetractinellids in Paleozoic seas ; while in the Trias, Jura and Cretaceous 

 these forms become important rock-builders, and play an active part in the 

 formation of hornstone, chalcedony and flint. In the Tertiary, spicules refer- 

 able to existing genera are common. 



The former distribution of the three best preserved sponge groups — the 

 Lithistids, Hexactinellids, and Calcisponges — is noteworthy. The living repre- 

 sentatives of the first two Orders inhabit deep or moderately deep water, while 

 the calcareous sponges predominate in shallow waters bordering the coast. 

 And hence, since fossil Calcisponges likewise occur almost entirely in marly, 

 clayey, or sandy strata of undoubted littoral origin, and are absent in lime- 

 stones where Lithistids and Hexactinellids predominate, it is piain that the 

 distribution of both fossil and Recent sponges has been occasioned by like 

 physical conditions. 



In the Cambrian occur the Lithistid genera Archaeoscyphia and Nipterella, 

 and in the Ordovician and Silurian of Europe and North America are found 

 a number of Tetracladina (Aulocopium) and Eutaxidadina forms {Astylospongia, 

 Palaeomanon, Hindia), together with a few Rhizomorina. In the Carboniferous 

 ßhizomorina and Megamorina are sparsely represented ; but in the Upper 

 Jurassic, and especially in the Spongitenkalk of Franconia, Swabia, Switzer- 

 land, and the Krakau district, the Lithistids exhibit an astonishing develop- 

 ment, and occasionally form thick beds. They occur only sparingly in the 

 Lower Cretaceous, but are abundant in the Pläner, Greensand and Upper 

 Cretaceous of Northern Germany, Bohemia, Poland, Galicia, Southern Russia, 

 England and France. The Tertiary being nearly everywhere made up of 

 shallow-water formations, the absence of Lithistids and Hexactinellids is not 

 surprising. They persist locally, however, as in the Upper Miocene of Bologna 

 and in the Province of Oran in Northern Africa. 



The ränge of the Hexadinellida is in every respect similar to that of the 

 Lithisiida. Beginning in the Upper Cambrian, they are represented in the 

 Ordovician and Silurian by peculiarly modified Lyssacina forms (Protospongia, 

 Phormosella, Cyathophycus, Palaeosaccus, Pledoderma, Pattersonia, Brachiospongia, 

 Didyophyton, Astraeospongia). The same group continues also through the 

 Devonian, where Didyophyton and its associates are conspicuous for their wide- 

 spread distribution in North America. A few aberrant Lyssacina, which Hinde 

 designates as Heteradinellidae, are found in the Carboniferous. During the 

 Mesozoic and Cenozoic eras the distribution of the Hexadinellida is nearly 

 identical with that of the Lithistida; although here and there beds occur 

 which are charged principally with Hexactinellids, and others chiefly with 

 Lithistids. 



Very different conditions are presented by the Calcisponges, among which 

 only the Pharetrones and Sycons are of geological importance. The oldest 

 calcareous sponges occur very sparsely indeed in the Middle Devonian and 

 Carboniferous Limestone. They appear in considerable diversity in the Alpine 

 Trias (St. Cassian and Seelandalp), but outside the Alps are almost wholly 

 absent. In the Jurassic they occur in marly beds of the Dogger (Ranville, 

 Swabia), and also in certain facies of the Malm (Terrain ä Chailles, Coral-Rag 

 of Nattheim, Sontheim, etc.) in Southern Germany and Switzerland. 



The Lower Cretaceous, particularly the Neocomian of Brunswick, the 

 Swiss Jura, and the Paris Basin, as well as the Aptian of La Presta, near 



