JUEASSIC. 75 



Family (?) PELAGID^ G-egenbaur. 



Genus ACRASPEDITES Haeckel. 



Aceaspedites antiquus Haeckel. 



PI. XLIV, fig. 2. 



Medusites antiquus Haeckel, 1865. Zeitschr. fiir wiss. Zoologie, Vol. XV, pp. 509-513, 



PL XXXIX, fig. 2. 

 Aeraspedites antiquus Haeckel, 1869. Zeitschr. fiir wiss. Zoologie, Vol. XIX, p. 559. 

 Aoraspedites antiquus Haeckel, 1880. System der Medusen, p. 647. 

 Acraspedites antiquus Ammon, 1886. Abhandl. Math.-phys. Classe Konigl. bayerischen 



Akad. Wiss., Vol. XV, p. 157. 



Dr. Haeckel states that little besides the " topography" of the specimen 

 is preserved. An acraspedote or phanerocarpous medusa. 



This is shown by the apparent structure of the genitalia. In il/. antiquus I 

 regard as such the lobe-like projections of the inner indented circle, which, as in all 

 acraspedotes, lie between the radial canals. In 21. deperditus, on the other hand, the 

 genitalia appear in the gentle spindle-shaped swellings in the middle of the radial 

 canals, the direct enlargement of which they produce, as with all craspedotes. 



1 inclined to put M. antiquus with the Pelagidie because of the simple, unbranched 

 radial canals, which, together with the marginal lobes, are 8 in number. If, however, 

 the radial canals were branched, the minor forks not being preserved, this form would 

 probably have to be placed with the Aurelid* or Cyanida-. 



.1/. deperditus probably goes with the Trachynemida 1 , and bears a strong resem- 

 blance to Rhopalouema. Both have eight equally strongly developed radial canals, 

 somewhat swollen in the middle. I believe that I can support this opinion also by 

 the fact that in Rhopalouema I find every radial canal accompanied and supported by 

 a double band of cartilage in streaks of greater consistency, which in any case would 

 tend to leave behind a distinct impression. The gelatinous mass of the umbrella also, 

 as well with the Trachynemida' as with the nearly related iEginida?, is distinguished 

 by an almost cartilaginous consistency, which renders them better adapted for pres- 

 ervation in a fossil condition than most other medusa?. One is then almost inclined 

 to regard the broad ring which surrounds the circle canal as the flat, expanded, and 

 pressed velum, which in the family of the Trachynemida? is strikingly thick and 

 strongly developed. Probably, however, here, as in M. antiquus, it is better to refer 

 this ring to the thickness of the gelatinous mantle itself, which, of necessity in the 

 case of an animal spread out flat and lying on the sea bottom, spread symmetrically 

 during its gradual entombment, while the whole body was slowly and symmetrically 

 compressed in the direction of the principal axis. In the case of M. antiquus, in which 

 the ring surrounding the circle canal (and also the actual rim of the umbrella cavity, 

 though much less broad) appears much more distinctly impressed, is this conclusion 



ids K 

 \>-u LIBRARY 5) 



