76 FOSSIL MEDUS®. 
all the more safe, since a velum is universally among the Acraspede only occasionally 
developed. That the fossil Medusites deperditus (of 70" diameter) is much larger 
than any living Trachynemide, at least any yet known (4™™-8"™ the maximum and only 
in a few cases, a few even below 1" in diameter), constitutes no argument against 
placing the former in this family, since in the nearest related group of the Geryonidee 
the greatest variation in size exists (1-3™™" to 50-60™™ in diameter).' 
Suborder RHIZOSTOM A Cuvier. 
Family LITHORHIZOSTOMEA Ammon. 
Genus RHIZOSTOMITES Haeckel. 
RHIZOSTOMITES ADMIRANDUS Haeckel. 
IL Sg IL RAHI, sis 2s 
Rhizostomites admirandus Haeckel, 1866. Neues Jahrbuch fiir Min., Geol. und Pal., 
pp. 261-282, Pl. V. 
Rhizostomites admirandus Haeckel, 1869. Zeitschr. fiir wiss. Zoologie, Vol. XTX, p. 557. 
Rhizostomites admirandus Brandt, 1871. Mém. Acad. imp. sci., St. Pétersbourg, 7th 
series, Vol. XVI, No. 11, pp. 1-18, Pl. I, figs. 1-4. 
Rhizostomites admirandus Haeckel, 1880. System der Medusen, p. 647. 
Rhizostomites admirandus Ammon, 1886. Abhandl. Math.-phys. Classe Kénigl. baye- 
rischen Akad. Wiss., Vol. XV, pp. 123-130; 158, 163-165, Pl. I, fig. 1; Pl. V. 
Dr. Haeckel’s original diagnosis of the species is as follows:* 
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" long and 
34™™ broad), and which are connate for the length of 20™™ in the middle of the inferior 
surface of the disk. (Probably each of the four principal arms was subdivided into two 
simple, short secondary arms.) Genital cavities 4, interradial between the basal por- 
tions of the 4 principal arms. The 4 sex organs are crescent-shaped elevations, 120™™ 
long and 15™™ broad, located on the periphery of the pouch-shaped genital cavities. 
A peripheral zone of the disk, of 70™™ 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 interradial), separated one from another by equal intervals, and 
thus forming 8 flat lobes (with probably 8 sense organs in the § 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™™ length and 9™™ 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. fiir wiss. Zoologie, Vol. XV, 1865, pp. 511-512. 
2 Neues Jahrbuch fiir Min., Geol. und Pal., 1866, p. 282. 
