JURASSIC. 79 



that his interpretation of this species as a rhizostome was correct, as his 

 study of the living Crambessa tagi had given him renewed assurance of the 

 correctness of the reference. He says: 



The oral under surface of the disk's center, or, more exactly, of the umbrella 

 stalk or oral disk, from whose periphery the four pairs of arms arise, shows in Cram- 

 bessa tagi the same markings as in B. admirandus, namely, a central mouth cross 

 surrounded by eight isosceles triangular areas. However, the significance which I 

 gave to these fields in Rhizostomites must be somewhat modified, for, as Crambessa 

 plainly shows, the four major, convex isosceles triangles which touch in the center are 

 not radial, but interradial. On the other hand, the four smaller, concave isosceles 

 triangles whose points converge with the ends of the limbs of the mouth-cross are not 

 interradial, but radial (more accurately, perradial). 



NOTES ON THE OBSERVATIONS OF DR. BRANDT' AND DR. AMMON ON RHIZOSTOMITES AND THE TWO 



SPECIES REFERRED TO IT. 



Dr. Brandt studied the material described by Dr. Haeckel and arrived 

 at the conclusion that Rhizostomites admirandus and R. lithograpliicus were 

 identical, the latter being only a younger specimen, as was suggested by 

 Dr. Haeckel in his remarks on the species. This resulted from his observa- 

 tions on the number of the marginal lobes, the width of the marginal zone, 

 and the arrangement of the oral cross. Dr. Brandt believes that Dr. Haeckel 

 was in error in his observations on the four crescentic mounds forming the 

 crescent ring. Dr. Haeckel regards these as representing the genital 

 pouches, but Dr. Brandt maintains that they are adventitious and without 

 structural significance. He locates the genital arms in four radially 

 located, depressed, elliptical figures, which Dr. Haeckel failed to observe. 



The fact that Dr. Haeckel regarded the fossils as secondary impressions, 

 while Dr. Brandt believes them to be direct impressions, affords a basis for 

 a definite interpretation of many of the future observations. 



Dr. Brandt calls attention to the fact that the configuration of the 

 mid-field in R. lithograpliicus corresponds remarkably with that of Cram- 

 bessa and must have the same significance. This is possible only on the 

 theory that the fossil is a direct impression. He is also inclined to believe 

 that Rhizostomites possessed, even at maturity, a mouth which was not 

 closed by the growing together of the margins; in which event it would 

 represent an intermediate fomi between the two acraspedote families. 



>Uelier fossile Medusen: Me"m. Acad. imp. sci. St. P6tersbourg, 7th series, Vol. XVI, No. 11, pp. 

 1-18, PI. I, fig.'l, 4. 



