82 FOSSIL MEDUS.E. 



is not the case in JR. lithographieus. B. lithographieus also has a broader 

 smooth zone than B. admirandus and on the radiating' seams forming the 

 8-armed oral cross numerous crinkled appendages appear in place that look 

 like tufts. In JR. admirandus these fringes are shorter and more scanty, and 

 the species also seems to be of larger form. 1 



After a careful study of the type specimen of Hexarhisites insignis, 2 Dr. 

 Amnion concludes that it agrees in all essential particulars with B. admirandus 

 and B. lithographieus. 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 B. admirandus 

 and B. lithographieus. His description of the genus Rhizostomites is as 

 follows (p. 155): 



Umbrella large, up to 400""" in diameter, round, with indications of 4 or S 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 sabgenital cavities. Four subgenital opercula on tbe margin of the not 

 especially wide ostia. Broad but sbort brachial trunks. Broad, strong arm disk, 

 hollowed out below. Cruciform mouth seam on the oral surface of the arm disk. Arras 

 of the mouth cross with crinkled appendages. Arms long and thin, probably with 

 tassel-shaped tuft on the lower end. Locality, Solenhofen and Eichstadt lithographic 

 slates, stage of Ammonites {OppeJiu) steraspis. 



Dr. Amnion has no doubt about the correctness of the reference of 

 Rhizostomites admirandus and B. lithographieus to the Rhizostomidpe. He 

 thinks that the fossil forms under discussion probably possessed long, 

 simple, unbranehed 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 lie regarded as only a lateral impression of Bhizos- 



1 Ueber none Exemplare von jurassiselien Metlusen : Abhandl. Math.-phys. Classe Konigl. baye- 

 rischen Akail. Wiss., Vol. XV, pp. 123-130, 158, 163-165, PI. I, tig. 2; PI. V. 

 2 Loc. oit., pp. 134-137. 



