596 The American Naturalist. [July, 
as highly exceptional, differing from any which has yet been 
described. I suggest for it the name Microcampana, the struct- 
ure of which is indicated below. Microcampana has six radial 
chymiferous tubes instead of four, eight or a larger number, as 
ordinarily occurs among its nearest allies. 
Among Hydromedusse the majority of genera have four radial 
tubes, but there are several, as Melicertum, which have eight, and 
still others, Zygodactyla, which have more than eight. Four, 
however, is the normal number in the majority of genera, and 
there are only two or three which have six. Microcampana is there- 
fore in the first place exceptional in the number of radial tubes. It 
has, moreover, a single club-shaped tentacle, resembling, it is true, 
that of Steenstrupia in the fact that it is single, but closely allied 
to those of Dipurena in anatomical characters. It is the only 
known genus which approaches Dipurena in the peculiar form of 
the tentacles. Unlike the last-mentioned genus, the apex of the 
bell is prolonged into a conical projection, through the middle of 
which, at least in its basal region, passes a small tube, the homo- 
logue of which is found in several genera where it is often the 
remnant of a former connection with the hydroid from which 
the Medusa has been formed by gemmation. The conical 
projection at the apex of the bell is exactly reproduced in two 
Atlantic genera, Stomatoca and Dinematella, neither of which, 
however, has less than two tentacles. To recapitulate, then, we 
have these extraordinary features in Microcampana, which are 
found in combination in none of the known Hydromedusae which 
have yet been described : there are six radial chymiferous tubes, 
a single tentacle, which is inflexible, and enlarged at its tip into a 
dumb-bell-shaped structure, and an apical projection on the bell 
penetrated by a median canal originating from the common junc- 
tion of the four radial tubes, and terminating blindly in the 
substance of the projection. 
It is probable that the size of this Medusa (it is barely an eighth 
of an inch in diameter), and the existence of but a single tentacle, 
are indications of immaturity. It may later be found that other 
tentacles are developed, and new affinities be sought for it. To 
this conclusion, the fact that a remnant of what may be a former 
