80 



FOSSIL MEDUSiE. 



Dr. Brandt defines the genus Rhizostomites as follows: 



Disk as large as 0.4 meter, with 128 marginal lobes, without marginal tentacles; 

 oral trunk rudimentary, usually the form of the oral disk, surrounded by eight arms. 

 Genital cavities, 4. Coelenteric central cavity simple, with sphero-quadratic roof. 

 Mouth opening late, perhaps never completely obliterated, cruciform, with 8 branches. 

 Locality, Eichstadt. Original in Eoyal Geological Museum at Dresden. 



Dr. Brandt gives a diagrammatic restoration of Rhizostomites, accom- 

 panied by a representation of one of the stages passed through in the 



Fig. 18. — Restoration of Rhizostomites. (After Brandt.) 



A. Diagrammatic vertical section of Rhizostomites in the direction of a main ray (R,, fig. 19). The dimensions of 

 this section correspond as accurately as possible to fig. 19 ; on account of the curvature it appears to he drawn on a smaller 

 scale. The dome of the umbrella and the cut-off mouth arms that are shown are restorations. The curvature of the whole 

 umbrella and the width of the central cavity are also hypothetic. 



B. The fossil of a rhizostomito supposed to be in course of production. 



C Approximate section of the impression of a large specimen of Rhizostomites admirandus. 

 (For explanation of lettering, see under fig. 19, opposite.) 



course of production of the fossil and by a section of the fossil impression, 

 as well as a view of the restoration from below. These are here repro- 

 duced (figs. 18, 19). 



Dr. Amnion admits the similarity between B. admirandus and B. litho- 

 graphicus, but in view of the fact that no intermediate forms have been 

 discovered he recommends that both species be retained, and gives the 

 following distinctive characters of each: In B. admirandus the furrowed 

 zone is a little wider than in B. lithograpliiciis ; the circular ridges in the 

 furrowed zone are more numerous, and they are equally distributed, which 



