328 PERIGONIMUS LINEARIS. 



GONOSOME. — GoNOPiioRES elevated on long peduncles ■wliicli are borne by the 

 creeping stolon. Medusa dome-shaped, with the vertical and transverse diameters 

 nearly equal ; manubrium reaching to about half the depth of the bell ; marginal 

 tentacles two, opposite, very extensile, with large basal bulbs ; two very small inter- 

 mediate marginal bulbs. 



fb/o/'/-.— Ilydranths and cojiiosarc, as well as the manubriuiu and marginal bulbs of the 

 medusa reddish orange. 



Development of gonosome. — Autumn. 

 Habitat. — Growing on the stems of other hydroids . 

 Bathjmetrical Distribution. — Coralline zone. 

 LocaJltij. — Torliay, G. J. A. 



This beautiful little hydroid was dredged from about twelve fathoms in Torbay, where it 

 invested the stems of Pliimularia sefacea. Though small, it is rendered very conspicuous by the 

 bright orange colour, not only of the hydrantlis, but of the ccenosarc, which is quite visible 

 through the delicate transparent perisarc. When about to detach itself from the trophosome the 

 medusa Ijursts through its uiembranous ectotheca, the remains of which may be usually seen 

 after its rupture still attached to the top of the peduncle. At the same tiuie, the two tentacles 

 which had been previously folded back into the cavity of the umbrella become liberated from their 

 confinement, and extend themselves in the surrounding water. The medusa, now divested of its 

 ectotheca, still remains for some little time attached to the summit of the peduncle, until at 

 length, after repeated convulsive efforts, it breaks loose from the trophosome, and henceforth 

 leads the life of a free zooid in the open sea. 



When the planolilast is at rest, or is floating listlessly in the water, the tentacles are usually 

 extended to a great length, and hang in the form of threads of extreme tenuity from the umbrella 

 margin ; but, on the slightest irritation, each tentacle is instantly drawn up assuming a beautiful 

 spiral in the act of contraction. The tentacles are also rolled into a spiral when the medusa, by 

 the contractions of its umbrella, is propelling itself through the surrounding water. 



8. Peeigonimus lineaeis, Alder. 



Atkactylis linearis, — Aider, Suppl. C'ntal., p. 6, pi. x, figs. 1, 2, 3. 



Perigonimus linearis, — Ailinan, in Ann. Nat. Hist, for May, 1864'. Hincks, Brit. Hydr. 



Zooph., p. 96, pi, xvii, fig. 3. 



TROPHOSOME.^ — Htdeocaulus consisting of unbranched (?) stems, which rise 

 at short intervals to the height of a quarter of an inch from a reticulated stolon ; 

 perisarc destitute of annulation, but slightly wrinkled near the base of the stems. 



