MUSEUM OF COMPARATIVE ZOOLOGY. 161 
of finding a case of commensalism, such as has been described in closely re- 
lated medusæ. 
A stage in the development of T. digitale younger than any yet mentioned 
is described below. 
The bell of the youngest Trachynema is flat, without apical projection, and 
covered with small papille. The surface is destitute of cilia. The chymif- 
erous tubes are broad, with smooth profile, and eight in number. Tentacles 
solid, stiff, with bright crimgon pigment spots in their distal extremities, and 
with the surface ciliated. The crimson pigment spots at the end of the ten- 
tacles are in irregular patches of color, and perhaps correspond with similar 
structures in the tentacles of Dipwrena. There are, however no such dumb- 
bell-like structures as are found in the latter genus. The number of tentacles 
is eight. The proboscis is short, destitute of a peduncle which is so completely 
developed in the adult. The mouth is cruciform, without oral tentacles, or 
knobs, and the lips are covered with lasso-cells. Color of the stomach, green- 
ish, with brown shades. Otocysts four, each with a single centrally placed 
otolith which is endodermic. 
In the past summer, all the intermediate stages between that described. and 
the adult were found. My drawings add nothing to the figures and account 
which Mr. Agassiz has published. The tentacles of the adult are covered with 
cilia, The male of T. digitale was not found. The sexual organs were always 
extended with ova, which resembled the eggs of other meduse in their trans- 
parency, and the possession of germinative dot and vesicle, both of which 
latter structures were plainly to be secn. 
Cunina discoides, n. s. 
Plate IT. Fig. 8, and Plate IV. Figs. 1, 2. 
The bell of C. discoides is flat, lens-shaped, transparent with smooth external 
surface, Radial tubes and extensions of the stomach wanting. No proboscis. 
The tentacles are solid, stiff, and borne at right angles to the vertical line of the 
bell. Number of tentacles fourteen. Below the bell is a gelatinous structure, 
collar-shaped, which hangs from the bell-margin as a circular ring, the width of 
which is about one half the height of the bell. This collar is crossed vertically 
by ribs (peroniæ), of which there are fourteen, each one arising from the base of 
the tentacle on the margin of the bell. "These structures appear to give sup- 
port to the tentacles, and have often been mistaken for vertical tubes. On the 
lower rim of the collar, which is called a sub-umbrella, are placed the otocysts. 
They contain each a single bright garnet-colored otolith, which is endodermic 
in its origin. Each otocyst is mounted on a short stalk. As the sub-umbrella 
hangs from the rim of the bell, so from the lower margin of the sub-umbrella 
is suspended a veil of about the same width as the sub-umbrella, Tt extends, 
however, at about right angles to the vertical axis, and forms a lower “floor” 
of the Cunina. The medusa is propelled in the water principally by the move- 
ments of this structure, The lower wall of the stomach is formed by a “ washer- 
VOL. VIII. — NO, 8. 
