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 

 PI. 6, 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. l t . 

 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 PI. 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 w r hat 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 PI. 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- 



