208 



CCELENTERATA. 



Hexarhizites, are considered as referable to the Acrasfieda, and to 

 be related to such living types as Rhizostoma. 



Of a somewhat more questionable nature are the singular bodies 

 from the Cambrian rocks of Sweden, to which Nathorst has given 

 the name of Medusites. These bodies are usually in the form of 

 four-rayed or five-rayed stars, or have the shape of four-sided or five- 

 sided pyramids the angles of which are more or less prolonged ; and 

 they have no actual organic structure. By Nathorst, however, they 

 are regarded, with much probability, as being produced by the in- 

 filling of the cavities of dead Jelly-fishes with mud or sand. On 

 this view the central pyramidal body of Medusites represents the cast 



Fig. 90. — The impression of the swimming-bell 01 a Jelly-fish (Rhizostomites admirandus) 

 preserved in the lithographic slate (Jurassic) of Eichstadt, in Bavaria, one-seventh of the natural 

 size. The missing parts are restored in outline. (Copied from Zittel.) 



of the gastric cavity of the polypite, while the four or five arms which 

 radiate from this represent casts of the radiating angles of the mouth. 

 In support of this view, Nathorst points to the known habit of certain 

 Jelly-fishes of lying at the bottom with the umbrella turned down 

 and the mouth directed upwards, in the position figured in fig. 89, 

 and he shows how this would naturally facilitate the filling of the 

 gastric cavity with mud. Moreover, Nathorst has shown that bodies 

 exceedingly similar in form and marking to the Cambrian Medusites 

 can be produced by taking casts of the internal cavities of fresh 

 specimens of Jelly-fishes in dilute plaster of Paris. 



Lastly, Nathorst has brought forward evidence to show that Jelly- 

 fishes are capable of producing various peculiar markings by their 



