PERIGONIMUS SERPENS. 327 



Colour. — Hydrantlis pale j-ellow, luaimbriuiu and marginal Indbs of medusa pale rcddisli, 

 perisarc yellowish brown. 



Development of </o)iosome. — .1 une. 



Ilahitai. — On an old Buccerium shell found in a rock-pool near low-water mark. 



liathjmetrical distribution. — Lammarian zone? 



Zoca%.— Eirth of Eorth, G. J. A. 



Perii/onimus vestitus was met with in the Eirth of Eorth in June, growing on an empty 

 Buccerium shell, where it was associated with IL/clractiuia ecldnaia. In the continuation of the 

 perisarc over the body of the hydranth, as well as in general habit, it comes very near to the 

 Periffoinmus j^cHiafus of Wright, from which, however, it difi'ers, judging from Dr. Wright's 

 description and figures, in its more developed liydrocaulus, in the thinner and more membranous 

 character of the perisarcal investment of the hydranths, in the position of the gonophores — which 

 are here borne almost exclusively on the liydrocaulus, only an occasional one being here and 

 there developed from the hydrorhiza, while in Veriyonimus palliatus they are described as being 

 confined to the hydrorhiza — and in the form of the medusa whose contracted codonostome gives 

 to the umbrella at the time of liberation an oviform shape, while in Peric/onimus palliatus the 

 umbrella does not become contracted towards the codonostome, and is accordingly nearly cylin- 

 drical in form. 



In medusas, about the tenth day after their liberation, the form had undergone consideraljle 

 change, the umbrella having become nearly spherical. No increase, however, had taken place in 

 the number of marginal tentacles. 



The trophosome is rendered particularly striking by the great dilatation of the stems, which 

 graduate into the body of the hydranths without any well-marked line of demarcation. In the 

 medusa the tentacles, which are very extensive, become rolled into an elegant spiral when 

 contracted. 



7. Pemgonimus serpens, Allman. 



Plate XI, figs. 7—9. 



Perigo.nimus serpens, — Allman, in Ann. Nat. Hist, for January, 1803. Hincks, Brit. Hydr. 



Zoopb., p. 93, pi. xvi, fig. 3. 



TROPHOSOME. — Htduocaulus consisting of short, simple stems, rising at sliort 

 intervals from a creeping reticulated stolon, and attaining a height of about two lines, 

 clothed with a very delicate transparent perisauc, which is destitute of annulatiou, and 

 loses itself at the base of the hydranths without forming distinct cup-like dilatations. 

 Hydeanths, with twelve or fourteen slightly alternating tentacles. 



