AGASSIZ AND MAYER: MEDUSA FROM AUSTRALIA. 17 
fore give a figure on Plate II., and a few details of its structure on Plate IIL., 
and also a brief description of the Medusa. 
When fully expanded the bell is rather flat, being five or six times as broad 
as it is high. The aboral surface is thickly covered with small granular 
papille, which give it a roughened appearance. The marginal lappets are very 
numerous, and their number is not very constant, but there are usually 16 
between each pair of sense organs, and as there are 8 sense organs, it would 
seem that the normal number of lappets is 128. 
An aboral view of one of the marginal sense organs is given in Figure 3, 
Plate III. An excellent figure of a longitudinal section has been given by 
von Lendenfeld (’88, p. 269, Fig. 66). 
Four thick pillars extend downwards from the ventral surface of the bell, 
and support the brachial disk, or subgenital porticus, as it is often called. The 
brachial disk, in turn, bears the eight mouth-arms (von Lendenfeld, ’88, p. 
239, Taf. 19, Fig. 10). A drawing of one of these mouth-arms is given in 
Figure 5, Plate III.; and it is lettered to correspond with von Lendenfeld’s 
Figure 36, Plate 23. The short, simple, upper portion of the arm is indicated 
by e, and a, 6, and d show the three wings of the lower arm; a being 
ventral, and 6 and d dorsal. A cross section of the lower portion of the arm 
taken at niveau ss, Figure 5, is given in Figure 6. Its lettering is similar to 
that of Figure 5. A view of the terminal portion of one of the mouth-arms 
showing the suctorial mouths, surrounded by double rows of small tentacles, is 
given in Figure 4. In life these tentacles keep in incessant motion, and by 
this means small particles of food are swept into the numerous suctorial 
mouths which open at intervals between the rows of tentacles. Good de- 
scriptions of the mouth-arms will be found in the papers of Grenacher and 
Noll (76),1 and of Hamann (’82).? 
The color of this medusa is normally cobalt-blue, but, as was discovered by 
von Lendenfeld (’84, p. 925), a species of Zodxanthella commonly infests it, 
forming dense clusters throughout the jelly ; and when this is the case the 
blue color is lost, and the medusa changes to a brown color, varying from that 
of white bread to that of coffee. Our figure (Plate II.) shows one of these in- 
fested medusz, and it will be seen that the only trace of the normal color is 
found in a faint blue line marking the uppermost regions of the suctorial 
mouths of the mouth-arms. In the estuary of the Brisbane River on May 21 we 
saw a great number of these meduse nearly every one of which was of a deep 
cobalt-blue, while now and then one was seen almost white in color, and still 
others showed intermediate stages between the deep blue and the white. We 
found the white or slightly brownish medusz in the Hawkesbury River near 
Sydney on April 4; in the harbor of Cairns, Queensland, April 27; and in the 
Brisbane River, May 21. We also found a small dark brown or coffee-colored 
1 H. Grenacher und F. C. Noll, 1876; Abhand. d. Senckenberg. Naturf. Gesell., 
Vol. X. p. 146, Plates I., IIT.-VII. 
2 O. Hamann, 1882; Jen. Zeit. fiir Naturwis., Vol. XV. pp. 243-285, 3 Plates. 
