76 FOSSIL MEDUSA. 



all the more safe, since a velum is universally among the Acraspedre only occasionally 

 developed. That the fossil Medusites deperditus (of 70" 1,u diameter) is much larger 

 than any living Trachyueuiidse, at least any yet known (4nim_gmm ^g maximum and only 

 in a few cases, a few even below l'" m in diameter), constitutes no argument against 

 placing the former in this family, since in the nearest related group of the Geryonidse 

 the greatest variation in size exists (l-3 mm to 50-60 ram in diameter). 1 



Suborder RHIZOSTOM^E Cuvier. 



Family LITHORHIZOSTOME.E Ammon. 



Genus EHIZOSTOMITES Haeckel. 



Rhizostomites admirandus Haeckel. 



PI. XL; PI. XLII, fig. 2. 



Rhizostomites admirandus Haeckel, 1866. Neues Jahrbnch fiir Min„ Geol. uud Pal., 



pp. 261-282, PI. V. 

 Rhizostomites admirandus Haeckel, 1869. Zeitschr. fiir wiss. Zoologie, Vol. XIX, p. 557. 

 Rhizostomites admirandus Brandt, 1871. Mem. Acad. imp. sci., St. Petersbourg, 7th 



series, Vol. XVI, No. 11, pp. 1-18, PI. I, figs. 1-4. 

 Rhizostomites admirandus Haeckel, 1880. System der Meduseu, p. 647. 

 Rhizostomites admirandus Ammon, 1886. Abhandl. Math.-phys. Classe Konigl. baye- 



rischen Akad. Wiss., Vol. XV, pp. 123-130; 158, 163-165, PI. I, fig. 1; PI. V. 



Dr. Haeckel's original diagnosis of the species is as follows: 2 



Medusa disk of 4 decimeters diameter. In the center 4 short and strong radial 

 major arms (branches of the gastral trunk, whose undivided base is 60" ,m long and 

 34"" u broad), and which are connate for the length of 20"" u in the middle of the inferior 

 surface of the disk. (Probably each of the four principal arms was subdivided into two 

 simple, short secoudary arms.) Genital cavities 4, iuterradial between the basal por- 

 tions of the 4 principal arms. The 4 sex orgaus are crescent-shaped elevations, 120 mm 

 long and 15 mm broad, located on the periphery of the pouch-shaped genital cavities. 

 A peripheral zone of the disk, of 70 mm breadth, with strongly developed ring muscles 

 of the subumbrella. Rim of the disk contracted at intervals so as to form 8 indenta- 

 tions (4 radial and 4 iuterradial), separated one from another by equal intervals, and 

 thus forming 8 flat lobes (with probably 8 sense organs in the 8 incisions). Besides 

 these 8 deep incisions in the umbrella margin, 120 other flatter radial incisions, by 

 which the latter is divided into 128 lobes of 22 mm length and 9 mm breadth. 



Dr. Haeckel gave a diagrammatic restoration of the under side of this 

 species, and also a vertical meridian section of the impression on the litho- 

 graphic limestone and of the medusa body, restored according to the 

 impression. 



1 Zeitschr. fur wiss. Zoologie, Vol. XV, 1865, pp. 511-512. 

 -Neues Jahrbuch fiir Min., Geol. und Pal., 1866, p. 282. 



