10 BRITISH FOSSIL SPONGES. 



46. 1846 Pictet, F. E. Traits elementaire de Paleontologie, Tome iv. 



Fossil Sponges are placed in the group of Aniorphozoaires of Blainville, 

 but it is considered doubtful whether they possessed true polyps, like Alcyonia, 

 or were without them. They are for the most part regarded as true horny 

 Sponges, but it is supposed that some genera, such as Siphonia, Jerea, 

 Myrmecium, and others, may have been provided with true polyps, and there- 

 fore belonged to Corals. 



47. 1840-47. Michelin, H. Iconographie Zoophytologique. 



Numerous species of Sponges from the Cretaceous and Jurassic strata of 

 France are described and figured. The descriptions are very brief and refer 

 merely to the superficial characters. Nothing definite is stated respecting the 

 nature of fossil Sponges, but they are apparently regarded as of the same 

 character as recent horny Sponges, which have become siliceous or calcareous 

 by fossilisation. They are mostly placed under the genera Spongia, Jerea, 

 Siphonia, &c, of previous authors. Two new genera, Guettardia and Turonia, 

 are proposed. 



48. 1847 Oswald, F. Ueber die Petrefacten von Sadewitz (Uebersicht Arbeit, und 



Verand. Schles. Gesell., p. 56). 

 Defines the Silurian genus Aulocopium, and places under it fourteen species, 

 the names only of which are given. Species of Scyphia and Tragos are simi- 

 larly named, but not described. 



49. 1847-48 Smith, J. Toulmin. The Ventriculidge of the Chalk (Ann. and Mag. 



Nat. Hist., vol. xx, pp. 73, 176, Pis. VII, VIII, and 2nd ser., vol. i, pp. 



36, 203, 279, 352, Pis. XIII— XVI). 

 The minute structure, though not the true nature of fossil hexactinellid 

 Sponges, is for the first time fully described. They are shown to consist of 

 thin, variously folded membranes, formed of a rectangular tissue of anastomosing 

 fibres, which at the points of intersection possessed hollow or octahedral 

 nodes. Several different kinds of tissue, that of the substance of the body, 

 a finer subdermal membrane, an exterior membrane, and that of the root-fibres 

 are described, the nodes of this latter not being hollow. The membranes are 

 not believed to have been originally of a mineral nature, but are regarded as 

 replacements by silica, iron, or lime of the original animal structures. The 

 fossils are regarded by the author not as Sponges, but as the skeletons of 

 polyzoa or ascidian polypes, in opposition to the opinion of Prof. John Morris 

 that they were Amorphozoa or Sponges. They are placed in the genera Ven- 

 triculites, Gephalites, and Brachiospongia. This last is obsolete, as it is only a 

 synonym of the previously constituted Plocoscyphia, Reuss, and Guettardia, Mich.. 



