422 M. K. A. Zittel on Fossil Hexactinellida. 



England, and Northern Germany. If we glance at the rest 

 of the fauna of the " Spongitenkalk," the abundance of 

 Brachiopods, Crinoids, and here and there of Foraminifera, 

 and the absence of true shore-haunting Gastropods and Lamel- 

 libranchs, are in favour of the production of these deposits 

 in deep water. The genera diffused in the Upper Jura 

 are Tremadictyon^ Craticularia, Sphenaulax, Sporadopyle^ 

 Verrucocoslta, Pachyteichisma, Trochoholus, Cypellia, Stau- 

 roderma, Casearta, Porospongia^ Porocypellia, and Staurac- 

 tinella. 



The distribution of the Hexactinellida in the Cretaceous 

 formation leads to a like result. In the older stages they are 

 entirely wanting or only occur singly. They appear in greater 

 abundance only in the Cenomanian group, in which the deposits 

 developed as "Planer" in the abundance of Foraminifera 

 and the scarcity of littoral animals bear the character of deep- 

 sea formations. North Germany, Saxony, Bohemia, Silesia, 

 and Poland contain the most fruitful localities for Middle- 

 Cretaceous Hexactinellida of the genera Ventriculites ^ Cysti- 

 spongia, Camerospongia^ Diplodictyon^ Plocoscypliia^ Pleuro- 

 stoma, &c. 



The greatest variety of fossil Hexactinellida and Lithistida 

 is furnished by the upper division of the Cretaceous formation, 

 but only by such deposits as, like White Chalk and certain 

 Chalk-marls, have long been regarded for many reasons as 

 deep-sea formations. In the littoral Chalk-tuff of Maestricht, in 

 the Coralline chalk of Faxoe, and in the Pisolitic chalk of the 

 Paris basin, Hexactinellida have hitherto been sought in vain. 

 The Cretaceous Hexactinellida are for the most part distin- 

 guished from the Palaeozoic and Jurassic forms by the octahe- 

 drally perforated crossing-nodes of the sexradiates, and belong 

 with but few exceptions to peculiar genera confined to the 

 Cretaceous formation [Ventriculites ^ Scltizorhahdus, Licmosi- 

 nion, Sporadosci^iia, RJiizopoterionj Cephalites, Lepidospongia^ 

 Leptophragma, Pleurostoma^Giiettardia, Coscinopora, Ophry- 

 stoma, Plocoscyjy/iia, Tremaholites, Etheridgia, Toulminia^ 

 Gamer ospongia^ Gystispongia^ Marshallia^ Callodictyorij Pleu- 

 ropCj Diplodictyon^ Cceloptychium) . Only the genera Crati- 

 cularia and Verrucocoelia are common to it and the Jurassic 

 formation. 



The deficiency of true abyssal deposits in Northern Em*ope 

 during the various phases of the Tertiary epoch may most 

 simply explain the deficiency of Hexactinellida in this forma- 

 tion. With the exception of small fragments of skeleton, 

 possibly belonging to the genera Farrea and Myliusia, from 



