24 
The largest medusæ-buds are fusiform or cylindrical, attached to 
the mother-polype by a pointed top. One of the largest measures 
from the point to the margin of the bell 0,40 mm., to the bent 
angle of the tentacle 0,490 mm., the greatest diameter of the bell 
being 0,192 mm.; another measures from its top to the distal end 
of the tentacle 0,62 mm. with a diameter of the bell of 0,232 mm. 
Genital cells I have not been able to observe; probably they will 
be found in the manubrium of later stages. 
The facts mentioned clearly show that our Hydroid has to be 
classified with the Gymnoblastic Anthomedusæ. Ås it does 
not in every point agree with any other form known to me I pro- 
pose to name it: 7chthyocodium sarcotretis. n. g., n. sp. 
Besides Protohydra, Microhydra and the hydroid stage of Lim- 
nocodium a few Hydroids are known, the hydranths of which are 
completely devoid of tentacles. Among undoubtedly gymnoblastic 
Anthomedusæ I have only found four mentioned; they are all 
epizoic like our new form, a fact which seems to me of some 
interest. Ichthyocodium shows most likeness to Hydrichthys mirus 
Fewkes. This form was found in 1887 at Newport by Fewkes 
(7 a and 5), growing on the skin of the fish Serio/a zonata Cuv. 
The colony is attached by a thin flat membrane, containing a mesh- 
work of tubes, to the skin of the fish in the neighbourhood of the 
anus. The membrane is said to be leathery, but without perisarc. 
From the tubes grow polypes of two kinds: 1) naked gonosomes, 
like clusters of grapes, consisting of an axial stem the terminal 
end of which is provided with a mouth-opening, and numerous 
branches; the latter are of the same structure as the stem, but 
closed terminally, where they carry clusters of medusæ-buds in 
various stages, up to medusiform bodies with two clumsy tentacles. 
The terminal part of the stem does not carry medusæ-buds, is 
devoid of tentacles, and its margin is entire. 2) Filiform polypes, 
supposed to be hydranths; they are described as flask-shaped bodies, 
resembling the palps of Siphonophores or the spiral zooids of Hy- 
dractinia (they are said to move in a similar way to the latter); 
