78 FOSSIL MEDUSA. 



of the subumbrella. On the contrary, they are short, much broken, unequally 

 separated one from the other, and for the most part bifurcate terminally and run out 

 into several gradually disappearing and diverging delicate furrows. These furrows 

 can very well be referred to the irregular furrows which exist between the super- 

 ficial folds of the fourfold elevation formed by the genitalia in the Rhizostoinidae and 

 other acraspedote medusa?. 



The third or smooth ring can be nothing else than that portion of the gelatinous 

 disk which immediately surrounds the genital cavity, and, in fact, forms its outer 

 wall. The completely even and smooth surface of this ring corresponds to the simple 

 nature of this portion of the umbrella, in which no especial structures are visible, and 

 where even the ring muscles of the subumbrella, which characterize the fourth ring 

 in so marked a manner, are lacking. Very important, too, is the negative circum- 

 stance that neither the smooth ring nor the two rings inclosing it are pierced and 

 interrupted in a radial direction by the prolongations of the radial arms. It can be 

 concluded from this that these were proportionally short and thick, similar to those 

 in the living Stomolophus; eveu were they as long as in Ehizostoma and in most 

 other Rhizostomidse, they need not necessarily have overlain merely the inner ring 

 (whose irregular figure they condition), but also the three outer rings. 



Beyond all doubt the 35 to 40 fine and concentric circular mounds which project 

 as low, three-cornered, prismatic ribs over the surface of the rings and leave the same 

 number of deep and sharp furrows between them, are to be referred to the muscle 

 rings of the subumbrella, which, in many Rhizostomidse, as well as in many other 

 Acraspedre (especially Cyaneidse), project in the form of strong, almost furrow-shaped 

 muscle rings over the under surface of the subumbrella. The muscular rings begin 

 in the outer portion of the smooth ring, become the strongest in the inner third of the 

 furrowed ring, and from there gradually fade away, so that the periphery of the disk 

 could only be contracted by comparatively weak ring muscles. The peripheral lobes 

 amount to 128 in the circuit of the entire disk. The very large number of these mar- 

 ginal lobes, which are characteristic of the Acraspedae, fits in especially with the 

 character of the Rhizostomida;, which are distinguished from the rest of the medusas 

 by the especially large number of these. The entire absence of all appendages to the 

 disk rim also speaks in a strong, negative manner for the rhizostomide nature of the 

 medusas. As a last form-character of the umbrella rim, likewise excellently fitting 

 our interpretation, can be offered the large, flat marginal lobes, which are indicated 

 on the under side of the impression by the strong radial indentations (y 3 ) and the 

 interradial indentations (.»). Both these invaginations, of which there must have 

 been eight in the whole disk edge, were surely deep incisions in which the four radial 

 and four interradial sense organs resided. 1 



Dr. Haeckel next discusses the systematic position of this species, and 

 refers it to the family Rhizostomidse 



In his review of the fossil medusas of the Jura, Dr. Haeckel 2 states 



1 Neues Jahrbuch fur Min., Geol. nnd Pal., 1866, pp. 273-280. 

 - Zeitschr. fur wiss. Zoologie. Vol. XIX, 1869, p. 557. 



