1034 The American Naturalist. [December, 
Measurements were difficult, but as nearly as I could make 
it out, the jelly fish was, at this time, about one-thirty-second 
of an inch in diameter. It was of a somewhat prolate dome- 
shape, and when seen from the polar aspect, the manubrium 
had a clearly quadrate appearance, from whose corners or 
lobes four radial canals curved downward to the marginal 
canal. At every point of junction occurred a single tentacle, 
and another of equal size was found midway between them. 
These eight tentacles (the only number as yet observed), al- 
ways pendent, were plentifully charged with thread cells, and, 
while susceptible of much variation in length, were not seen 
much longer than one-half the diameter of the disc. 
As to temperature, it is obvious that the water of the jars in 
which this Medusa was developed, must have had nearly that 
of the surrounding atmosphere, with its diurnal changes, say 
from 60° to 85° at this season: during the winter, in our 
heated rooms, the temperature is probably more uniform. The 
hydroid form, in Tacony Creek, being but a few inches below 
the surface, must be subjected frequently to a temperature 
at or below the freezing point. 
It is quite improbable that under the present artificial condi- 
tions, any Meduse will attain full maturity this season. It is 
therefore manifestly unsafe to compare their minute size and 
general appearance with the totally dissimilar drawings given 
us of Limnocodivm, where the latter had attained a diameter 
of about one-halfaninch. The full life-history of the organism 
must, therefore, be again left imperfectly recorded; but I am 
happy to be able to state that my friend, Dr. Charles B. Daven- 
port, of Harvard University, has consented to undertake the 
further technical study of it from material we have recently 
collected; and the drawings, etc. left by Dr. Ryder and to 
hope that many points, now obscure, may, through his efforts, 
be solved. : 
To aid the search of others for this—probably the most 
primitive ccelenterate—it may be well to state that, in my 
experience, I have only found M. ryderi in a natural condition, 
living as a messmate among colonies of Bryozoa that may be 
considered almost perennial in habit, where its own disabili- 
