88 FOSSIL MEDUSZ. 
R. 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 medusz, and suggests 
the advisability of calling H. insignis a synonym of hk. admirandus. 
Genus LEPTOBRACHITES Haeckel. 
LEPTOBRACHITES TRIGONOBRACHIUS Haeckel. 
Leptobrachites trigonobrachius Haeckel, 1869. Zeitschr. fiir wiss. Zoologie, Vol. XIX, 
pp. 544-548, 558, Pl, XI. 
Leptobrachites trigonobrachius Leuckart, 1870. Jahresberichten ueber Acalephe: 
Archiv. fiir Naturgesch., Wiegmann, Vol. II, p. 280. 
Pelagiopsis leuckarti Brandt, 1871. Mém. Acad. imp. sci. St. Pétersbourg, 7th series, 
Vol. XVI, No. 11, pp. 18-26, Pl. IL. 
Leptobrachites trigonobrachius Haeckel, 1880. System der Medusen, p. 647. 
Leptobrachites trigonobrachius Ammon, 1886, Abhandl. Math.-phys. Classe Konig]. 
bayerischen Akad. Wiss., Vol. XV, p. 158. 
Dr. Haeckel’s description and remarks, freely translated and condensed, 
are as follows:' 
The only clearly recognizable portions of this medusa are 8 three-cornered, 
slender, oral arms, and a portion of the lobed umbrella rim, as well as the peripheral 
contour of the whole disk and a genital gland. 
The disk of the living animal probably possessed a tolerably high bell, and the 
consistency of the gelatinous substance seems to have been inconsiderable. There 
appear to have been 48 marginal lobes in all, though only 16 are discernible on even a 
very careful inspection. 
The deep indentations in the margin, for the sense organs, which were found in 
other fossil meduse, are not to be distinctly seen here, though probably present. 
Marginal tentacles appear to have been entirely lacking. 
The 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 middie 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 arms is not simply pointed, 
or rounded off, but terminates in a lancet-shaped body, 24™™ 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 
! Zeitschr. fiir wiss. Zoologie, Vol. XIX, 1869, pp. 545-547. 
