82 FOSSIL MEDUS®. 
is not the case in R. lithographicus. RR. lithographicus also has a broader 
smooth zone than R. admirandus and on the radiating seams forming the 
8-armed oral cross numerous crinkled appendages appear in place that look 
like tufts. In R. admirandus these fringes are shorter and more scanty, and 
the species also seems to be of larger form." 
After a careful study of the type specimen of Hexarhizites insignis,” Dr. 
Ammon concludes that it agrees in all essential particulars with R. admirandus 
and R. lithographicus. It possesses the oral subgenital lids, and, aside from 
its hexameral symmetry, it has no points of difference. He is also inclined 
to consider it possible that Leptobrachites trigonobrachius is the same form, 
crushed laterally, as that which produced the oral impressions in 2. admirandus 
and R. lithographicus. His description of the genus Rhizostomites is as 
follows (p. 155): 
Umbrella large, up to 400" in diameter, round, with indications of 4 or 8 principal 
lobes. Umbrella rim subdivided into a large number of marginal lobes. Besides the 
somewhat larger lobes, smaller ones can be distinguished. Indentations of the rim for 
marginal sense organs. Circle canal situated in the external third of the umbrella 
surface. Sixteen radial canals. Subumbrella with strong muscular expression. <A 
powerful ring muscle. Between the oral disk and the muscle zone on the inner side, 
a strong circular depression, perhaps with the structural significance of an inner ring 
canal. Four subgenital cavities. Four subgenital opercula on the margin of the not 
especially wide ostia. Broad but short brachial trunks. Broad, strong arm disk, 
hollowed out below. Cruciform mouth seam on the oral surface of the arm disk. Arms 
of the mouth cross with crinkled appendages. Arms long and thin, probably with 
tassel-shaped tuft on the lower end. Locality, Solenhofen and Hichstadt lithographic 
slates, stage of Ammonites (Oppelia) steraspis. 
Dr. Ammon has no doubt about the correctness of the reference of 
Rhizostomites admirandus and R. lithographicus to the Rhizostomide. He 
thinks that the fossil forms under discussion probably possessed long, 
simple, unbranched arms. The evidence for this rests upon the facts 
(1) that if the arms were fleshy, manifold, and much branched, the 
fossils, which are largely gastral impressions, would not be so clearly 
impressed and their lines so unbroken and undisturbed; (2) the specimen 
of Leptobrachites trigonobrachius, which has long, simple arms terminating in 
a bristly spatulation, can be regarded as only a lateral impression of Rhizos- 
1 Ueber neue Exemplare von jurassischen Medusen: Abhand]. Math.-phys. Classe Kénigl. baye- 
rischen Akad. Wiss., Vol. XV, pp. 123-130, 158, 163-165, Pl. I, fig. 2; Pl. V. 
2Loce. cit., pp. 184-137. 
