MUSEUM OF COMPARATIVE ZOOLOGY. 161 



of finding a case of coramensalism, such as has been described in closely re- 

 lated medusae. 



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 papillae. The surface is destitute of cilia. The chymif- 

 erous tubes are broad, with smooth profile, and eight in number. Tentacles 

 solid, stiff, with bright crimson 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 Dipurena. 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 bro^\^l 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. dirjitale was not found. The sexual organs were always 

 extended with ova, which resembled the eggs of other medusae in their trans- 

 parency, and the possession of germinative dot and vesicle, both of which 

 latter structures were plainly to be seen. 



Cunina discoides, n. s. 



Plate II. 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 bonie at right angles to the vertical line of the 

 bell. Number of tentacles fourteen. Below the beU 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 (peroni(e), 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. It 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. 11 



