PORIFERA 49 



common ; amongst the Lithistids the following occur : — 

 Seliscothon, Verruculina, Scytalia,Doryderma,8ind Siphonia; 

 the Hexactinellids are represented by Graticularia, Verru- 

 coccelia, Guettardia, Ventriculites, Cephcdites, Plocoscyphia, 

 and Camerospongia; the Calcarea are represented by 

 Porosphcera. In the Tertiary formations detached spicules 

 are sometimes abundant, but few perfect sponges have 

 been found. 



w. p. 



