80 FOSSIL MEDUSZ&. 
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. Ccelenteric central cavity simple, with sphero-quadratic roof. 
Mouth opening late, perhaps never completely obliterated, cruciform, with 8 branches. 
Locality, Eichstiidt. Original in Royal 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 
Fia. 18.—Restoration of Rhizostomites. (After Brandt.) 
A. Diagrammatic vertical section of Rhizostomites in the direction of a main ray (Rj), fig. 19). The dimensions of 
this section correspond as accurately as possible to fig. 19; on account of the curvature it appears to be 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 rhizostomite supposed to be in course of production. 
C. Approximate section of the impression of alarge 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. Ammon admits the similarity between R. admirandus and R. 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 R. admirandus the furrowed 
zone is a little wider than in R. lithographicus; the circular ridges in the 
furrowed zone are more numerous, and they are equally distributed, which 
