12 INTEODUCTION. 



at Upware in Cambridgeshire, are filled with these sponges. The minute structural 

 characters of the sponges from these beds has only been partially preserved ; but 

 traces of the spicules can usually be distinguished in thin microscopic sections. The 

 following genera are represented — VeHicilUtes, Peronella, Elasmocoglia, Conocoslia, 

 Cor//nella, Synopella, Oculospongia, Elasmostoma, and Pharetrospongia. 



(II.) Upper Green Sand and Chloritic Marl. — In beds of this series at Warminster 

 in Wiltshire, Blackdowu and Haldon in Devonshire, the Isle of Wight, near Folke- 

 stone, and near Havre in France, sponges are very numerous. In some localities 

 the beds are largely made up of spicules of Monactinellid and Tetractinellid sponges 

 with an admixture of Lithistid and Hexactinellid spicules, and resemble those 

 already mentioned from tlie Lower Green Sand. These detached spicules have been 

 described and figured by Mr. Carter * and Mr. Parfitt f . The Lithistid sponges of 

 this series are particularly abundant, and, as a rule, retain their siliceous composition ; 

 but as they are usually preserved in a very hard siliceous matrix, it is only by 

 preparing sections that the structure can be distinguished. The genera of Lithistids 

 comprise Cheneniopora, Jereica, Doryderma, Ilolodicfyon, Pachypoterion, NemaUnion, 

 CartereUa, Phymatella, Trachysycon, Siphonia, Hallirhoa, Jerea, Polyjerea, Kalpi- 

 nella, and Bhopalospoiiyia. The Hexactinellids are less numerous in proportion to 

 the Lithistids, and belong to the genera Craticidaria, Stauronema, Sestrodictyon, 

 Guettardia, Eiihrochus, Plocoscyphia, and 8clerokaJia. Calcisponges are numerous 

 in some localities: the most important place for them is Essen, in Prussia; they 

 are also present at Warminster and near Havre. They mostly belong to the same 

 genera as those in the Lower Green Sand; but the majority of the species are 

 difi"erent. 



(III.) Chalk Marl, Gray Chalk, and Lower Chalk. — Beds of this series near Dover, 

 Folkestone, and in the Isle of Wight contain a well-marked group of sponges, for 

 the most part of the same genera as those in the underlying Upper Green Sand and 

 Chloritic Marl, but of diff"erent species. The siliceous skeleton of these sponges has 

 been replaced by calcite, and their present condition is very unfavourable for deter- 

 mination. The sponges from the Chalk Marl of the Isle of Wight, however, remain 

 siliceous, and can be partially cleaned from the matrix by acid. The Lithistids of 

 this series of beds are included in the genera Stachyspongia, Phymatella, Siphonia, 

 Jerea, Nelumhia, Polyjerea, and Thamnospongia. The Hexactinellids associated in 

 the same beds with the Lithistids belong to the genera Craticidaria, Strephinia, 

 Verrucocoelia, Stauronema, Leptopliragma, Guettardia, Sestrocladia, Ophrystoma, 

 and Plocoscyphia. I do not know of any Calcisponges from this division. 



(IV.) Upper Chalk, including Maestricht Chalk. — Siliceous sponges abound in this 

 division of the Cretaceous system. In this country they are of most frequent 



* Annals and Mag. Nat. Hist. ser. 4, vol. vii. p. 112. 

 t Transactions of the Devonshire Association, 1870. 



