JURASSIC. 89 
stomach. On the other hand, one can recognize with moderate certainty the quadrant 
of a mound-shaped ring lying on the upper left-hand portion of the disk center. It 
appears as a crescent-shaped body, everywhere 10" broad, whose two rounded ends 
are about 60" apart. It is almost absolutely certain that this is a sexual gland. 
This is indicated by its characteristic position and also by its crescentic shape, which, 
as in many acraspedotes, is rounded off at both ends. 
the end of the first, shows that there was a complete 
genital ring. 
The affinities of this medusa are not known with 
certainty, since we can learn nothing of its whole 
gastrovascular system, the form of the mouth, of 
the stomach, of the radial canals, ete. It can be 
asserted, however, that it belongs to the higher 
meduse, the acraspedote or phanerocarpous medu- 
se. Proofs of this exist in the marginal lobes and 
the oral arms. Of the two groups which Agassiz 
distinguishes in this division, the Rhizostomze and 
the Semostomee, our fossil medusa probably belongs 
to the former. This can be deduced with great cer- 
tainty from the number and structure of the arms, in 
spite of the fact that the characteristic polystomy 
and the lack of a central mouth, by which the Rhizo- 
stom are distinguished from all other medusz, are 
not to be recognized in the obscure impression in 
Another gland, beginning near 
Fic. 21.—Contour drawing of Leptobrachi- 
tes trigonobrachius, reduced and restored. 
(After Brandt.) 
A, B, C, B, four distinctly recognizable 
mouth arms; D, problematic fifth arm; M, 
expression of the thickness of the umbrella; 
, lower surface of the umbrella; O, ring 
zone, with the entrances into the genital 
cavities; P, place of transition of the um- 
brella into the stem; Q, wallofthestem; R, 
transition of the stem into the bases of the 
mouth arms; a, boundary of the outside sur- 
face of the umbrella; b, boundary of the in- 
ner surface of the umbrella; ¢, ec’, ec’, c/’’, mar- 
ginal lobes; /, outline of the ccelenteric cen- 
tral cavity; 7, lips of the mouth and side 
plates of the mouth arms; 0,0’, 0’, entrances 
into the genital cavities. 
question. Most of the rhizostomes possess 8 similar 
oral arms of a three-sided prismatic form, while a 
similar number and structure of the arms very sel- 
dom exists among the semostomes. Furthermore, 
if our fossil medusa had possessed marginal tenta- 
cles, one would expect to find at least some trace of 
them between the lobes of the margin. But this 
is not the case. Since these structures are charac- 
teristically absent from the rhizostomes, while among the semostomes they are devel- 
oped in greater or less numbers, the balance of evidence seems to be in favor of placing 
LL trigonobrachius with the rhizostomes. Furthermore, it can be concluded, by a pro- 
cess of exclusion, that it stands among the Leptobrachid. 
Leuckart, in reviewing Haeckel’s diagnosis of this species, states that 
he has examined the types and can not discern the characters of a rhizos- 
tomide, nor the 8 arms, and that he favors the views expressed in the forth- 
coming work of Brandt. 
Dr. Brandt’s observations on L trigonobrachius are so at variance with 
those of Dr. Haeckel that he has felt it necessary to propose for the species, 
