126 M. K. A. Zittel on Fossil Lithistidce. 



tons. Even in the specimens from the celebrated sponge- 

 localitj of Sutmerberg near Goslar, most of the siliceous 

 skeletons of Lithistidaj show the commencement of a pseudo- 

 morphosis. If thej are placed in dilute muriatic acid, a por- 

 tion of the sponge-body is sometimes dissolved, and, indeed, 

 generally the surface and the parts nearest to the surface. 

 The rest of the skeleton consists of silica ; in fact, the interior 

 is not unfrequently thoroughly impregnated with flint. 



If these siliceous parts of the skeleton be more closely ex- 

 amined, they generally show a dull corroded surface, and the 

 finer adornments of the small skeletal corpuscles have for the 

 most part disappeared. Optically they diiSer from living and 

 other Cretaceous Lithistidce in that they possess nearly the 

 same refractive power as Canada balsam, and therefore must 

 be examined in glycerine, oil, water, or some such medium. 

 A similar behaviour is shown by the Lithistidee from certain 

 Upper- Jurassic localities in the Franco-Swabian Jura 

 (Schauergraben, near Streitberg, Uetzing in Franconia, So- 

 zenhausen, Pappelan, and Sontheim in Wlirttemberg) and in 

 the Cracow district (Wodna, Kobilany, Luszowice) ; only 

 here, as a rule, the calcification has advanced much further 

 than at the Sutmerberg, so that during treatment with acid 

 large portions of the sponge-body are destroyed. The re- 

 maining parts behave optically in the same way as the Hex- 

 actinellida^ occurring in the same locality*. 



In general the pseudomorphosis of the Upper-Jurassic 

 Lithistidse is not confined to particular parts of the sponge- 

 body, but the whole skeleton is usually converted throughout 

 into calc-spar. In such forms the interspaces between the 

 skeletal particles and the canals are without exception filled 

 with stone, and, indeed, usually with limestone. In the Franco- 

 Swabian Spongitenkalk of the White Jura /?, y, and S, most 

 of the Lithistidge are completely calcified, and it is only now 

 and then that a few siliceous skeletal corpuscles are obtained 

 in the residue after treatment with acid. The same state of 

 preservation is shown by the Lithistidse from the upper and 

 lower Spongitenkalk of Switzerland (Baden and Binnensdorf ' 

 beds) and of the French Jura, the valley of the Rhone, the 

 Cevennes, and the neighbourhood of Niort. In the Planer of 

 Saxony and Bohemia also the calcified skeletons predominate. 

 I have already attempted to give an explanation of this re- 

 markable phenomenon in the first section of these " Studies " 

 ('Annals,' October 1877, p. 266). 



It is remarkable that, in the pseudomorphosis of an origi- 



• See the tirst section, 'Annals,' Oct. 1877, pp. 262, 26.3. 



