PALEONTOLOGY. 387 



which the horny fibres had been changed to stone by means of 

 the processes of petrefaction. Similarly, the works of Geinitz, 

 Klipstein, Pusch, Reuss, Quenstedt, and Roemer increase 

 the knowledge of the endless diversity of form presented by 

 sponges, but add little to a scientific comprehension of their 

 structure. 



A notable position in the older literature of sponges is 

 taken by the two short memoirs of Toulmin Smith (1847-48), 

 wherein the structure of the Ventriculites from the white chalk 

 is fairly accurately represented. Owing, however, to the fact 

 that the nearest allies among living sponges, the Hexactinellids, 

 were unknown at the time of his investigations, Smith drew 

 fallacious inferences regarding the nature and systematic 

 position of these fossils. He compared them with Bryozoa. 



In the year 1851, D'Orbigny devised a badly-arranged 

 scheme of classification for fossil sponges, upon the basis solely 

 of external features. He called all fossil sponges " Petro- 

 spongiae," and contrasted them with recent sponges, ascribing 

 to fossil sponges an originally stony skeleton composed of 

 calcareous fibres. According to D'Orbigny, the petrospongiae 

 form a curious and extinct sub-division of the sponges. This 

 erroneous conception of D'Orbigny's was shared by Fromentel, 

 but the latter author, in differentiating genera and species, made 

 use of differences in the canal system and in the kinds of pores 

 and openings at the surface. Friedrich Roemer followed 

 Fromentel's method, and he differentiated between sponges 

 with fenestrated skeletal structure and sponges with a skeleton 

 composed of " worm-shaped fibres." Pomel also made careful 

 observations of the skeletal structures so far as those could be 

 distinguished with the naked eye or by the aid of a hand-lens. 



The deep-sea investigations of the last part of the nineteenth 

 century initiated a new era in the investigation of sponges, 

 recent and fossil. Wyville Thomson, the leader of the 

 Challenger Expedition, was the first to point out the similarity 

 in the structures of fossil ventriculites and living silicispongiae. 

 In 1870, Oscar Schmidt, by the method of etching Jurassic 

 and Cretaceous specimens, demonstrated in fossil forms the 

 presence of certain skeletal structures similar to those of 

 existing hexactinellids and lithistids. Nevertheless the fossil 

 sponges still presented an apparently distinct and well-defined 

 group, until almost simultaneously Zittel and Sollas resolved to 

 apply Nicol's method and prepare thin slices of the fossil 



