SPONGES 1 1 1 



Laubu [Tr.] ; *Cehjphia, Pom. [Tr.] ; ^Himatella, Z. [Tr.] ; * Peronidella, 

 Zeise { = Feronella, Z.) [Jur. Cret.] ; * Elnsmocoelia , Roein. [Cret.] ; 

 *Conocoelia, Z. [Cret.] ; *Euini>ho>ieIl(i, Z. [Jur.] ; *Corynella, Z. 

 [Tr. Jur. Cret.] ; ^Myrmerium, Goklf. [Tr. Jur.] ; *Inobolia, Hinde 

 [Ool.] ; *Lyinnorea, Lanix. [Jur.] ; *Sttllispongia, d'Orb. [Tr. Jur.] ; 

 *Trucliymnia, Hinde [Jur.] ; *SestrogtomeUa, Z. [Jur. Cret.] ; *Blastinia, Z. 

 [Jur.]; *Syno]iell<(, Z. [Cret.]; *0cnlisj}07igi(i, From. [Jur. Cret.]; *Crispi- 

 spongia, Qst. [Jur.] ; ^Elaimiostoma, From. [Jur. Cret.] ; * RhapMdonemay 

 Hinde [Cret.] ; * Pharetrospnngia, Soil. [Cret.] ; *Holcosponrpa, Hinde 

 [Ool.] ; *Fachytilodi((, Z. [Cret.] ; *Eanffia, Zeise [Jur.] ; *Euzittelia, 

 Zeise [Jur.]; *Stramhergia, Zeise [Jur.]; *Thalamopora, Eoem. [Jur.]; 

 (Pobjstcgamnae, ^tt.) ; *Verticillites, Defr. {= Tremacystia), [Cret.], (Fig. 

 14, A). Sdb-Family 2. Lithoninae, Rft". With body spicules united 

 by fusion into a rigid framework ; fibres confined to cortical layer. 

 Genus — Petrostroma, Dod. (Fig. 14, B). 



Many of the fossil forms included here under Dialytinae will very 

 likely prove, when better known, to belong to the Lithoninae. 



Incerti si'dis — *ProtosycoH, Z. [Jur.]; {Sycettidae 1). 



CLASS II. HEXACTINELLIDi\. 



The Hexactinellida or Triaxonia are a group of sponges character- 

 ised in the first instance by the possession of siliceous spictiles of the 

 triaxon type, which are therefore primitively six -rayed. This 

 fundamental structural peculiarity is correlated with a very uniform, 

 and at the same time a very characteristic type of organisation, 

 rendering the group one almost as sharply marked off from other 

 sponges as are the Calcarea. 



To judge by the abundance of fossil remains, the Hexactinellids 

 seem to liave been a very abundant group at all times. At the 

 present day they are almost confined to the deep sea, but in this 

 region they are a widespread, and apparently flourishing group. 

 It is to their peculiar habitat, however, that must be ascribed our 

 still very great ignorance with regard to many points, especially of 

 their histology and life-history. 



1. Canal Sjiateni. — The embryonic development of the Hexac- 

 tinellid sponges is not known ; but very young specimens, still 

 without an osculum, have been described by Schulze in his 

 great monograph [21], from which it would appear that the 

 starting-point for the development of the canal system in these 

 forms is a stage which has advanced considerably beyond the 

 Ohjnthu^i condition, and conforms more to the second type of canal 

 system (Fig. 76 ; cf. Fig. 44), the gastral layer being folded to 

 form flagellated chambers. The wall of the sponge even in these 



* Fossil forms: Tr. = Trias, Jur. = Jurassic, Ool. = Oolite, Cret. = Cretaceou.'s. 



