134 



COELENTERATA 



PHYLUM II 



in the fossil state. Nevertheless, under exceptionally favourable conditions, 

 as, for instance, in the Upper Jurassic Lithographie Stone of Bavaria, and in 

 the Middle Cambrian shales of British Columbia, impressions of these delicate 

 organisms are sometimes preserved, which admit of precise determination. 



The best preserved and at the same time the most abundant species is 

 Rhizostomites admirandus Haeckel, belonging to the Acraspedote family of 

 Rhizostomidae (Fig. 212). Impressions also occur in flinty concretions of the 

 Upper Cretaceous, which are most nearly referable to the Medusae. Of a 

 more questionable nature are the organisms occurring in the Cambrian 

 sandstone of Lugnaes, Sweden, described by Thorrell under the name of 



Rhizostomites admirandus Haeck. Lithographie stone ; Eichstädt, Bavaria. 1/7 natural size. 

 (Missing parts restored'in outline.) 



Spatangopsis, but assigned by Nathorst to the Acalephs. In the same strata 

 also are found those peculiar fucoidal structures known as Eophyton, which are 

 commonly supposed to be of vegetable origin. Nathorst has brought forward 

 evidence, however, to show that these may really have been produced by the 

 trails of Jelly-fishes. Here also should be noticed the forms described by 

 Nathorst as Medusites, frona the Lower Cambrian of Sweden, and regarded by 

 this author as casts of the gastric cavity of Jelly-fishes. 



In 1898 a valuable monograph on fossil Medusae was contributed by 

 Walcott, and in 1911 our knowledge of these organisms was increased in 

 important respects by the same author, as a result of his studies of remarkably 

 well-preserved specimens from the Cambrian of British Columbia. 



Handl., 1881, vol. xix.—Ammon, L. v., Ueber jurassische Medusen. Abhandl. Bay. Akad. 1883, 

 vol. xvii. — Brandt, A., Ueber fossile Medusen. Mem. Acad. Imp. St-Petersb., 1871, 7tli ser., 

 vol. xvi. — Pohlig, H., Altpermische Medusen. Festschrift zum 70ten Geburtstage K. Leuckarts, 

 U^2.- -Walcott, ö. D., Fossil Medusae. U. S. Geol. Surv. Monogr., xxx., 1898.— /c^em, Middle 

 Cambrian Holothurians and Medusae. Smithson. Mise. Coli., 1911, vol. lix. No. 3. — Mayer, 

 A. 0\, The Medusae of the World, i.-iii. Carnegie Inst. Wash,, Pub. No. 119, 1911. 



