66 COELENTERATA SPONGIAE CLASS i 



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 limestones 

 where Lithistids and Hexactinellids predominate, it is plain that the distribu- 

 bution of both fossil and recent sponges has been occasioned by like physical 

 conditions. 



In the Cambrian occur the Lithistid genera Archaeosci/phia and Nipterella, and 

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

 of Teiracladina (Aulocopium) and Eutaxidadina forms (Astylospongia, Palaeomanon, 

 Hindia), together with a few Rhizomoiina. In the Carboniferous Ehizomorina 

 and Megamorina are sparsely represented; but in the Upper Jurassic, and 

 especially in the Spongitenkalk of Franconia, Swabia, Switzerland, and the 

 Krakau district, the Lithistids exhibit an astonishing development, and 

 occasionally form thick beds. They occur only sparingly in the Lower 

 Cretaceous, but are abundant in the Planer, Greensand, and Upper Cre- 

 taceous 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, for instance, in the 

 Upper Miocene of Bologna, and in the Province of Gran in Northern 

 Africa. 



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

 Lithistida. 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, Astmeospongia). 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 Li/tsarina, which Hinde 

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

 Mesozoic and Cenozoic eras the distribution of the HexartinrUidn 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 a Chailles, Coral-Rag of 

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



The Lower Cretaceous (particularly the Neocomian of Braunschweig, the 

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

 Neuchatel, and Farringdon, Berkshire ; and also the Middle Cretaceous (Ceno- 

 manian) of Essen, Le Mans, and Havre, are characterised by an abundance of 

 well-preserved Pharetrones, and a lesser number of Sphinctozooid Sycons. In 

 the Tertiary, however, both groups are wanting, although the existence of 



