JURASSIC. 83 
tomites admirandus or R. lithographicus ; (3) in a specimen of R. 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 Crambesside. 
Analogies with the latter are also shown in the arm disk, which in most 
Crambessidze 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 
Crambessidze. Dr. Ammon 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 Pilemidee, 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 of the eruci- 
form mouth, on the under side of the thick, strong oval, can have the same 
structure in the Pilemidze as in the Crambessidze; 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 
Pilemidze and Crambessidz, the Tetrademnia and the Monodemnia, and to 
represent a peculiar extinct family of the rhizostomous medusz. 
RHIZOSTOMITES LITHOGRAPHICUS Haeckel. 
Pee chest be xe ies. 12. 
Rhizostomites (?) lithographicus Haeckel, 1866. Neues Jahrbuch fiir Min., Geol. und 
Pal., pp. 282-286, Pl. VI. 
Rhizostomites (?) lithographicus Haeckel, 1869. Zeitschr. fiir wiss. Zoologie, Vol. XIX, 
p. 908. 
Rhizostomites (?) lithographicus Brandt, 1871. Mém. Acad. imp. sci., St. Pétersbourg, 
7th series, Vol. X VI, No. 11, pp. 3-13, Pl. I, fig. 2. 
Rhizostomites (?) lithographicus Haeckel, 1880. System der Medusen, p. 647. 
Rhizostomites (?) lithographicus Ammon, 1886. Abhandl. Math.-phys. Classe Kénigl. 
bayerischen Akad. Wiss., Vol. XV, pp. 108-122, 158, 161-162, Pl. 1; PJ. III, fig. 1; 
TAL VU IG IOYG tiles Ge 
