86 FOSSIL MEDUSAE. 



Genus HEXARHIZITES Haeckel. 



Hexarhizites insignis Haeckel. 



PL XLIII, fig. 1. 



Hexarhizites insignis Haeckel, 1874. Jenaische Zeitscbr., Vol. VIII, pp. 312-323, PL X. 

 Hexarhizites insignis Haeckel, 1SS0. System der Medusen, p. 017. 

 Hexarhizites insignis Amnion, 1S86. Abliandl. Matb.-phys. Classe Konigl. bayei'ischeu 

 Akad. Wiss.,Vol. XV, pp. 134-137, 158. 



Dr. Haeckel defines the genus Hexarhizites as follows: x 



Medusa disk made up of antiineres, wbicb group tbemselves symmetrically on 

 botb sides of tbe central moutb seam. Tbe transverse 2 lipped moiitb opening 

 (almost?) completely grown together in tbe middle of a regular 12-sided, concave moutb 

 disk, wbicb is formed by tbe bases of 6 strong, forking, connate moutb arms. Tbe 12 

 arm branches short, without further bifurcation. Six iuterradial genital pouches, over 

 tbe entrance to which a centripetal subgeuital lid projects. Twelve radial canals; 

 at the end of these, 12 marginal sense organs. Xo marginal tentacles. Umbrella rim 

 split up into numerous lobes. 



character of Hexarhizites insignis. — Umbrella circular (27°'" in diameter), with a regular 

 12-sided moutb disk on the oral side, whose diameter measures a third of the former 

 (9 cai ). Mouth disk formed by the basal portion of 6 short, broad oral arms grown 

 together, which later divide up into two forks. Tbe seams of union of tbe oral arms 

 unite in tbe center of the moutb disk to form a 12-rayed figure, composed of G small 

 perradial and G larger iuterradial areas, whose boundaries (the "seams of union") 

 project as sharp ridges. The oral seam forms a transverse fissure, upon which two 

 iuterradial areas abut. On either side of this tbe remaining ten areas are so arranged 

 that tbe regular Grayed form of the medusa passes over into tbe amphitbect- 

 symmetrical form. On the periphery of every iuterradial area is a genital pouch, 

 shaped like an isosceles triangle with a base 6 cm long, over the entrance to which an 

 arched subgeuital flap projects radially inward, 4 C,U distant from tbe center. Tbe 

 smooth zone, 3 cm wide, which surrounds this genital zone is separated from the mar- 

 ginal zone (likewise 3 cm broad) by a circular ring canal 21 cm iu 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 iu 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 zoues can be distinguished, the 

 outer of wbicb is designated the marginal zone or muscle zone, the median as the 

 smooth zone or smooth ring, and tbe inner, tbe one which incloses tbe middle field, 

 as tbe genital zone. 



Tbe mid-field (g-g&) 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 



1 Jenaische Zeitscbr., Vol. VIII, 1874, pp. 312, 314-315. 



