86 FOSSIL MEDUS 4. 
Genus HEXARHIZITES Haeckel. 
HEXARHIZITES INSIGNIS Haeckel. 
Pl, XMM, fig. 1. 
Hexarhizites insignis Haeckel, 1874. Jenaische Zeitschr., Vol. VIII, pp. 312-323, Pl. X, 
Hexarhizites insignis Haeckel, 1880. System der Medusen, p. 647. 
Hevarhizites insignis Ammon, 1886. Abhandl. Math.-phys. Classe K6nigl. bayerischen 
Akad. Wiss., Vol. XV, pp. 134-137, 158. 
Dr. Haeckel defines the genus Hexarhizites as follows: * 
Medusa disk made up of 6 antimeres, which group themselves symmetrically on 
both sides of the central mouth seam. The transverse 2-lipped mouth opening 
(almost?) completely grown together in the middle of a regular 12-sided, concave mouth 
disk, which is formed by the bases of 6 strong, forking, connate mouth arms. The 12 
arm branches short, without further bifurcation. Six interradial genital pouches, over 
the entrance to which a centripetal subgenital lid projects. Twelve radial canals; 
at the end of these, 12 marginal sense organs. No marginal tentacles. Umbrella rim 
split up into numerous lobes. 
Character of Hexarhizites insignis Umbrella circular (27°™ in diameter), with a regular 
12-sided mouth disk on the oral side, whose diameter measures a third of the former 
(9°). Mouth disk formed by the basal portion of 6 short, broad oral arms grown 
together, which later divide up into two forks. The seams of union of the oral arms 
unite in the center of the mouth disk to form a 12-rayed figure, composed of 6 small 
perradial and 6 larger interradial areas, whose boundaries (the ‘‘seams of union”) 
project as sharp ridges. The oral seam forms a transverse fissure, upon which two 
interradial areas abut. On either side of this the remaining ten areas are so arranged 
that the regular 6-rayed form of the medusa passes over into the amphithect- 
symmetrical form. On the periphery of every interradial area isa genital pouch, 
shaped like an isosceles triangle with a base 6°™ long, over the entrance to which an 
arched subgenital flap projects radially inward, 4°™ distant from the center. The 
smooth zone, 3°™ wide, which surrounds this genital zone is separated from the mar- 
ginal zone (likewise 3°" broad) by a circular ring canal 21° in diameter. Sharply 
impressed ring muscles on the oral surface of the marginal zone; 144 shallow lobes on 
the umbrella edge; 12 marginal bodies or sense organs; 12 radial canals. 
As in Rhizostomites admirandus, we distinguish in the Hexarhizites disk a cen- 
tral circular mid-field and several concentric zones, which surround it in a circle. 
Even when viewed from above three such rings or disk zones can be distinguished, the 
outer of which is designated the marginal zone or muscle zone, the median as the 
smooth zone or smooth ring, and the inner, the one which incloses the middle field, 
as the genital zone. 
The mid-field (g-gg) is a regular 12-sided, flat depression, and is a counter proof 
of the flat, excavated oral disk of the medusa. The margin of the mid-field passes over 
‘ Jenaische Zeitschr., Vol. VIII, 1874, pp. 312, 314-315. 
