42 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. 



Gallery X. From this island and from Tennessee comes the noteworthy 

 Octactinellid, Astraeospongia. 



Wall-case The Devonian of North America yields casts of Dictyo- 

 phyton, a Lyssacine Hexactinellid. 



Wall-ease From the Triassic strata of St. Cassian there is a series 

 of small Calcispongiae, which have been referred to Stclli- 

 spongia, Corynella, and other genera of Pharetrones. 



Wall-ease The Upper Jurassic rocks of Wiirtemburg and Switzer- 

 8a, 8b. land, known as the White Jura, contain a large number of 

 Hexactinellida and Lithistida, some layers being mainly 

 composed of these sponges. They retain their outer form, 

 but, in nearly all, the siliceous skeleton has been replaced by 

 calcite. Examples of numerous genera are exhibited. 



Among the Cretaceous sponges, special notice should be 



^^^-c^se taken of the fine specimens of Coeloptyclimm from the 

 Westphalian Upper Chalk, and of the exquisite series of 



Wall-ease Hexactinellida and Tetractinellida from the Upper Senonian 

 Chalk of Hanover prepared by Dr. A. Schrammen by carefully 

 dissolving out the siliceous skeleton from the calcareous rock : 

 alone among fossil sponges do these present the beauty so 

 frequent in the skeletons of recent forms. Those illustrated 

 in the accompanying Plate III are : (1) Calyptrella temcis- 

 sima ; (2) a species of Rhizopoterion ; (3) SiJoradoscinia 

 Declicni, the upper figure showing the interior with the 

 canals, into which open the ostia seen in the lower figure ; 

 (4) Aphrocallistes alveolites. 



Wall-ease Tertiary sponges are so rare that one must not overlook 



7a, corner, the Calcispongiae, Tretoccclix, Bactronella, and Flectroninia, 

 w^hich are modified Pharetrones from the Eocene of Australia. 



The Trustees issued in 1883 a Catalogue of the Fossil 

 Sponges in the Museum by G. J. Hinde, who has also begun 

 a Monograph of the British Fossil Sponges, published by the 

 Palaeontographical Society (1887, 1888, 1893). See further 

 E. A. Minchin, Section on Sponges in Lankester's " Treatise 

 on Zoology," London, 1900. 



