AMOKPHOZOA. 7 



other families with calcareous spicula, The horny sponges 

 appear to be more abundant now than in the ancient seas, but 

 their remains are only recognisable in those instances where 

 they were charged with silicious spicula, 



M. d'Orbigny enumerates 36 genera and 427 species of 

 fossil sponges ; and this is probably only a small proportion 

 of the actual number in museums, as the difficulty of deter- 

 mining the limits of the species is very great, and many 

 remain undescribed. 



Palceospongia and Acanthospongia occur in the lower Silu- 



>*v\ 



Fig. 2. 



Amorphozoa ; Bkizopoda. 



i. Siplionia pyriformis, Golclf. ; Greenland, Blackdown. 



2. Guettardia Thiolati, D'Arch. ; U. Chalk, Biarritz. 



3. Ventriculites radiatus, Mant. ; U. Chalk, Sussex. 



4. Manon osculiferum, Phil. ; U. Chalk, Yorkshire. 



5. Fusulina cylindrica, Fisch. ; Carboniferous, Russia. 



6. Flabellina rugosa, D'Orb. ; Chalk, Europe. 



7. Lituola nautiloidea, Lam. ; Chalk, Europe. 



8. Nummulites nummularia, Brug. ; Eocene, Old World. 



9. Orhitoides media, D'Arch. ; U. Chalk, France. 

 10. Ovulites margaritula, Lam. ; Chalk, Europe. 



rian ; and Stromatopora, with its concentrically laminated 

 masses, attains a large size in the Wenlock limestone. Ste- 

 ganodictyum, Sparsisjjongia, and species of Scyphia, are found 



