JURASSIC. 83 



tomites admirandus or E. lithographicus ; (3) in a specimen of II. lithographicus 

 there is a long furrow originating- near the center and extending irregularly 

 over the disk, terminating in an expansion, which can be interpreted as the 

 impression of an arm, like the arms of Leptobrachites trigonobrachius. He 

 considers that these characters indicate an affinity with the Crambessidse. 

 Analogies with the latter are also shown in the arm disk, which in most 

 Crambessidse is said to be a large, thick, gelatinous sheet of a quadrate form 

 (seldom octagonal), on the under side of which is the characteristic crumpled 

 seam of the cruciform mouth. There are also subgenital opercula, and 

 there can be readily presupposed the existence of four subgenital cavities 

 instead of the single central cavity situated on the ventral floor, as in the 

 Crambessidse. Dr. Amraou considers that this view could be maintained 

 even if the oval figures, which otherwise would be referred directly to the 

 cavity, should be taken for the impression of gonads. 



This structure of four subgenital cavities and four subgenital opercula 

 speaks, on the other hand, for a relationship with the Pilemidse, in which 

 every thickening of the rim of the ostium (subgenital lid) is shown in the 

 clearest form; likewise the muscle rim by which, in this family, the firm, 

 hard substance of the gelatinous disk is indicated. The seam ot the cruci- 

 form mouth, on the under side of the thick, strong oval, can have the same 

 structure in the Pilemidse as in the Crambessidse ; but there are here present 

 strong, heavy, bushy arms which can not have existed in the Jurassic 

 rhizostomites. The fossil forms thus seem to stand midway between the 

 Pilemidse and Crambessidse, the Tetrademnia and the Monodemnia, and to 

 represent a peculiar extinct family of the rhizostomous medusse. 



Rhizostomites lithographicus Haeckel. 

 PI. XLI, tig. 1; PI. XLII, tigs. 1, 2. 



Rhizostomites (?) lithographicus Haeckel, 1866. Neues Jakrbucb fur Min., Geol. unci 



Pal., pp. 282-286, PI. VI. 

 Rhizostomites (?) lithographicus Haeckel, 1869. Zeitsckr. filr wiss. Zoologie, Vol. XIX, 



p. 558. 

 Rhizostomites (?) lithographicus Brandt, 1871. Mem. Acad. imp. sci., St. Petersbourg, 



7tk series, Vol. XVI, Xo. 11, pp. 3-13, PI. I, fig. 2. 

 Rhizostomites (?) lithographicus Haeckel, 1880. System der Meduseu, p. 647. 

 Rhizostomites (?) lithographicus Ammon, 1886. Abkaudl. Matk.-pkys. Classe Konigl. 



bayeriscken Akad, Wiss., Vol. XV, pp. 108-122, 158, 161-162, PI. I ; PI. Ill, fig. 1 ; 



PI. Ill; PL IV, fig. 3. 



