88 FOSSIL MEDUSAE. 



B. lithographicus, and concluded that, apart from the hexameral symmetry, it 

 agreed in all essential particulars with those species. He calls attention to 

 the great number of anomalies existing among recent medusae, and suggests 

 the advisability of calling H. insignis a synonym of It. admirandus. 



Genus LEPTOBRACHITES Haeckel. 

 Leptobrachites trigonobrachius Haeckel. 



Leptobrachites trigonobrachius Haeckel, 1869. Zeitsckr. far wiss. Zoologie, Vol. XIX, 



pp. 544-548, 558, PL XLI. 

 Leptobrachites trigonobrachius Leuckart, 1870. Jakresberichten ueber Acalepha?: 



Arcbiv. far Naturgesch., Wieginann, Vol. II, p. L'SO. 

 Pelagiopsis leuckarii Brandt, 1871. Mem. Acad. imp. sci. St. Petersbourg, 7tb series, 



Vol. XVI, No. 11, pp. 18-20, PI. II. 

 Leptobrachites trigonobrachius Haeckel, 1880. System der Medusen,p. 047. 

 Leptobrachites trigonobrachius Ainmou, 18S0. Abbaudl. Matb. -phys. Classe Konigl. 



bayeriscben Akad. Wiss., Vol. XV, p. 158. 



Dr. Haeckel's description and remarks, freely translated and condensed, 

 are as follows: 1 



Tbe only clearly recognizable portions of tbis medusa are 8 three-cornered, 

 slender, oral arms, and a portion of the lobed umbrella rim, as well as tbe peripheral 

 contour of tbe whole disk and a genital gland. 



Tbe disk of the living auimal probably possessed a tolerably high bell, and tbe 

 consistency of the gelatinous substance seems to have been inconsiderable. There 

 appear to have been 48 marginal lobes in all, though only 10 are discernible on even a 

 very careful inspection. 



The deep indentations in tbe margin, for the sense organs, which were found in 

 other fossil medusae, are not to be distinctly seen here, though probably present. 

 Marginal tentacles appear to have been entirely lacking. 



Tbe oral arms, the best-preserved portions of the entire organism, are 8 in number 

 and very slender. At their base they are only slightly enlarged, and toward the end 

 they are only slightly tapering. Through the middle of each arm, throughout its entire 

 length, runs a sharp, strongly projecting keel, on both sides of which the surface of 

 the arms declines toward the limiting contour, in the shape of oblique planes. Plainly, 

 this appearance indicates a three-sided prismatic form for the arms, as is common to 

 many rhizostomes. The arms seem, conformably to their slenderness, to have been 

 very flexible. The structure of the terminal portion of the arms appears to be very 

 important, especially in connection with the determination of the systematic position 

 of the medusa. The. outer or under (distal) portion of the anus is not simply pointed, 

 or rounded off, but terminates in a lancet-shaped body, 24 mm long. 



Owing to poor preservation, no certain conclusions can be drawn as to the 

 structure of the umbrella, the relation and form of the arm bases, or the mouth and 



1 Zeitschr. fiir wiss. Zoologie, Vol XIX, 18H9, pp. 545-547. 



