INTEODUCTIOX. 11 



period have been discovered. In strata of this age at Schafberg, Austria, Prof. 

 Zittel discovered beds of agglomerated spicules of Monactinellid, Tetractinellid, and 

 Hexactinellid sponges, which have been described and figured by Dunikowski *. In 

 cherty strata in Glamorganshire there are also numerous spicules. 



Jurassic System. — The sponges of this division are very numerous. The Monac- 

 tinellidae are represented by the single freshwater genus SpongiU.a, from Purbeck 

 strata in the south of England. The Lithistidse and Hexactinellidge are met with 

 in great numbers in different zones of the Upper Jurassic, in South Germany, 

 Switzerland, Eastern France, and in the vicinity of Cracow ; but they are entirely 

 absent in the strata of corresponding age in England. In some of the Portland beds, 

 however, there are large masses and nodules of flint, which probably indicate the 

 former existence of sponges in these strata ; and in some of these flints detached 

 spicules of Tetractinellid sponges are still preserved. The Lithistids of the Upper or 

 White Jura of Germany -belong to the following genera — Cneinidiastrum, Coral- 

 lidiwn, Hyalotragos, Pyrgochonia, Leiodorella, Platychonia, Placonella, MegalitMsta, 

 Cylindrophyma, Melonella, and Lecanella. The Hexactinellids are included in the 

 genera Tremadictyon, Craticularia, Splienaulax, Sporadopyle, VerrucococUa, Pachy- 

 teichisma, Trochobolus, Phlyctcenium, Cypellia, Staurodcrma, PorocypelUa, Casearia, 

 Porospongia, and Toulminia. In most of these siliceous sponges the original skeleton 

 has been replaced by calcite ; but in the strata of some localities the sponges yet 

 retain their siliceous structure in very perfect preservation. There are but few 

 calcareous sponges in the English Jura; but they abound in the Jurassic strata of 

 France and Germany, and have been referred to the genera Eudea, Peronella, 

 Eusiphonella, Corynella, Myrmecium, Lymnorea, StelUspongia, Sestrostomella, Blas- 

 tinia, Oculospongia, Crispisjiongia, Pharetrospongia, and Protosycon. 



Cretaceous System. — Both the Siliceous and Calcareous sponges may be said to 

 attain their maximum development in this period. In this country there are four 

 well marked zones in the Cretaceous rocks, each characterized by distinctive groups 

 of sponges. They are (I.) the Lower Green Sand, (II.) the Upper Green Sand and 

 Chloritic Marl, (III.) the Chalk Marl, Gray Chalk, and Lower Chalk, and (I^'.) 

 the Upper Chalk, including the Maestricht Chalk. 



(I.) Lower Green Sand. — Very few recognizable siliceous sponges occur in tliis 

 division ; but in sandstone strata at Haslemere, in Surrey, there are thin beds nearly 

 entirely composed of the spicules of Tetractinellid sponges, with an admixture of u 

 few Hexactinellid and Lithistid forms ; some of these latter are sufficiently charac- 

 teristic to be referred to the genus Mastosia. Similar beds of sponge-spiculcs also 

 occur in the Ilils sandstone in Westphalia. On the other hand, the calcareous 

 sponges are very numerously represented in this series, not only in this country, but 

 in France, Germany, and Switzerland. The gravels of Farringdon in Berkshire, and 



* Spongien, Radiolarien uud Foramiixiferen der unterliassischen Schiohten vora Schafberg. Wien, 1882. 



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