INTRODUCTION. 13 



occurrence in the Chalk near Flamborough Head in Yorkshire, and in the southern 

 and south-western counties. The strata of this age in Westphalia, Hanover, and 

 Brunswick contain large numbers of sponges, which retain their original structure 

 in most beautiful preservation. On the other hand, the Upper Chalk sponges of 

 this country are in a very unfavourable condition of preservation, and it is only in 

 those which have been preserved in the interior of flints that the spicular structure 

 can be satisfactorily ascertained. In the Flamborough forms, as already mentioned, 

 the siliceous spicules are fused together, whilst in the sponges from Surrey, Kent, 

 Sussex, and elsewhere to the South of England, the siliceous skeletons are either 

 replaced by peroxide of iron or completely dissolved away. The following genera 

 of Monactinellids are present in this division — Eeniera, Scolioraphis, Dirrhojmlum, 

 Acanthoraphis, Opefionclla, and CUona. The Tetvactinellid sponges have been 

 referred to the genera Ophiraphidites, Tethyopsis, Stellctta, Geodia, Thenea, and 

 Pachastrella. The Lithistid sponges include the genera BoUdium, Chonella, Selis- 

 cothon, Verruculina, Stichophyma, Jereica, Scytalia, Stachysfongia, Pachinion, Dory- 

 derma, Heterostinia, Carterella, Isoraphinia, Phymatella, Aulaxinia, Callopcqma, 

 Trachysycon, Siphonia, Jerea, Nelumhia, Bolospongia, Thecosiphonia, Calymmatina, 

 Turonia, Thamnospongia, Pholidocladia, Ragadima, Plinthosella, and Phymaplectia. 

 The genera of Hexactinellids comprise Craticularia, Verrucocoelia, Lepiopliragma, 

 Pleurostoma, Guettardia, Coscinopora, Aphrocallistes, Ventriculites, Schizorhabdus, 

 Ehizopoterion, Sporadoscinia, Polyhlastidium, Cephalites, Porospongia, Cincliderma, 

 Plocoscyphia, TremahoUtes, Etheridgia, Toulminia, Camerospongia, Cystispongia, 

 Callodictyon, Porochonia, Becksia, Biplodictyon, CceloptycMum, Stauractinella, and 

 Hyalostelia. 



If the siliceous sponges are exceedingly numerous in the Upper Clialk, the 

 calcareous forms, on the other hand, are comparatively rare. In the South of 

 England examples of the genera Elasmostoma and Pharetrospongia are not uncommon 

 in the Chalk and in flints ; and in the Chalk of Maestricht there are species of 

 Synopella, Oculospongia, and Elasmostoma. 



Eocene System. — Numerous detached spicules of Monactinellid, Tetractinellid, 

 Lithistid, and Hexactincllid sponges have been discovered by Rutot* in the Eocene 

 Sandstone of Brussels. 



Miocene System. — Lithistid and Hexactinellid sponges have been discovered by 

 Pomelf in strata of this age in the Algerian province of Oran, and by Manzoni J in 

 beds of Molasse sandstone in the provinces of Bologna and Modena in Italy. The 

 numerous genera which Pomel has constituted on the characters of the canal- 



* Annales de la Sooiete Malacologique de Bclgique, tome ix. 1874 ; and Carter, Ann. and Mag. Nat. Hist. 

 ear. 4, vol. xix. p. 382. 



+ Deacription des Animaux fossiles de la Province d'Oran, .5'' fascicule, 1872. 

 X La struttnra mioroscopica delle Spugne silicee del Miocene medio, 1882. 



