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 Archacoscyphia and Nipterella, and 
in the Ordovician and Silurian of Europe and North America are found a number 
of Letracladina (Aulocopium) and Eutavicladina forms (Astylospongia, Palacomanon, 
Hindia), together with a few Lhizomorina. In the Carboniferous Rhizomorina 
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 Pliner, 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 Oran in Northern 
Africa. 
The range of the Heaactinellida 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, Plectoderma, Pattersonia, Brachiospongia, 
Dictyophyton, Astraeospongia). The same group continues also through the 
Devonian, where Dictyophyton and its associates are conspicuous for their wide- 
spread distribution in North America. A few aberrant Lyssacina, which Hinde 
designates as Heteractinellidae, are found in the Carboniferous. During the 
Mesozoic and Cenozoic eras the distribution of the Hezxactinellida 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 4 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 
