OX A FRESHWATER MEDUSA FROM RHODESIA. 431 
E. T. Browne, in his description of the Niger specimens (9), 
remarks that to judge from the appearance of the medusa© 
“ the mouth is incapable, owing to the shortness of the lower 
wall of the stomach, of completely closing up.” 
I do not consider the point just dealt with to be one of 
systematic importance. The first medusa I described had a 
widely open mouth similar to that of L. tanganicae, and I 
think it highly probable that a more exhaustive study of living 
examples of the latter species will reveal the fact that the 
manubrium is capable of great changes in shape. It must 
also be remembered that the specimen I have been describing 
is a young one, and the figures given by Gunther of similar- 
sized individuals of L. tanganicae suggest that at this stage 
the manubrium has greater powers of contractility than in 
the adult. 1 
Although much torn, the umbrella edge of this individual is 
not at all macerated, and the structure of the marginal region 
forms the main distinguishing feature of the Rhodesian 
species. In this form the “ nettle-ring,” instead of forming a 
broad continuous band round the margin of the umbrella as in 
L. tanganicae, is considerably narrower and, moreover, dis- 
continuous, the masses of stinging-cells being grouped round 
the bases of the tentacles and giving rise to distinct bulbous 
swellings similar to the tentacle bulbs which have been 
described in manv Trachymedusae, e.g. Gonionemus murbachi 
(PI. 42, fig. 2). ' 
The tentacle-bulbs are equally well developed in the third 
of the four medusae entrusted to me by Mr. Rousselet. This 
individual is very incomplete, and is represented by a sectant 
of the bell and part of the manubrium ; as in the medusa 
just described the umbrella-margin is well preserved, and both 
show very clearly another structural difference between 
L. rliodesiae and L. tanganicae. 
In the Tanganyika species there is no obvious relation 
between the arrangement of the marginal sense-organs and 
that of the tentacles, whereas in the Rhodesian medusae such 
1 C f . Gunther (10), p. 646, text-fig. 172. 
