10 THE HYDROIDS. 
Gonosome : —The gonothecae occur both on the hydrorhiza and on the 
hydrocaulus. They are sessile, or nearly so, nearly cylindrical in the distal 
half, tapering to the base, strongly curved, having a terminal opening in the 
centre of a diaphragm-like membrane. A somewhat unusual type of a young 
medusa with four main tentacles was found in one of the gonothecae (see 
PIG, fig... 7). 
Habitat : — Serial Number of Haul, 4742. Latitude, North, 0°.3.4". Lon- 
gitude, 117°. 15.8’ West. Trawl, 2320 fms. 
As this colony was attached to a pteropod shell still containing its maker, 
it was probably taken in the tow. 
This is a beautiful form, and because of its perfect freedom from other 
animals and plants and from all dirt, it is an especially favorable and enjoy- 
able object for study. The most marked feature is the deep fluting of the 
distal portion of the hydrothecae, which is well shown in PI. 7, fig. 4. 
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Something of a transverse constriction occurs in some of the hydrothecae, — 
always a little below the transverse median line ; it appears in some of the 
hydrothecae on each of several hydrocauli, as represented on Pl. 6. The 
size of the hydrothecae varies much, a few very small ones, the peduncles 
of which arise from the hydrorhiza, being only one half the length of the 
largest. 
A second colony of what is apparently this same species was taken in the 
tow net in a surface haul at the locality recorded under serial number 4657, 
Latitude, South, 7-12.5’. Longitude, West, 84° 9. Tow at 300 fms. This 
colony is also attached to an inhabited shell (see Pl. 7, fig. 5). It will 
be seen that the differences of the number of annulations and the curvature 
of the gonothecae are far too slight to be of specific value. 
Obelia (?) sp. 
Plate 5, Figs. 5-7. 
Trophosome : — Stems simple, unbranched, rising from a simple creeping 
stolon, with four to six annulations at the base and the same number imme- 
diately above the origin of each peduncle. The hydrothecae occur alter- 
nately on opposite sides of the stem, borne on short, stout peduncles of four 
to six annulations ; their length is about two and a half times their greatest 
breadth, they taper gradually to the base, the diaphragm is well marked, 
the rim bears about sixteen pointed teeth arranged in pairs, the space be- 
