Hydroida from Iceland. lo3 



shaped, strongly ribbed calycles, narrowed very decidedly 

 towards the somewhat overhanging rim, which bears four 

 short teeth, and is very little depressed between them ; the 

 latter has large, straight-walled, somewhat broad-based calycles, 

 not shai-ply carijiated transversely, narrowing very gradually 

 towards the margin, which bears four very prominent and 

 pointed teeth, and is deeply sinuated between them. 



The ramification of Gf. geniculata is peculiar. Branches 

 are given off rarely at right angles to the stem, springing 

 from the base of a calycle ; sometimes two branches are 

 developed at opposite points on the same internode. Not un- 

 frequently the internodes comprising a shoot do not all lie in 

 the same plane ; on the lower portion the calycles face one 

 way and a different way above. 



Notwithstanding the similarity in some points to S. tenellaj 

 I believe the present to be a well-established form, which. may 

 properly be ranked as a species. 



Amongst the Icelandic dredgings S. geniculata is not un- 

 common. 



Sertularella tenellaj Alder. 



I have also met with a characteristic specimen of this 

 species. 



EXPLANATION OF THE PLATES. 

 Plate VI. 



Fig. 1. Lafoea grandis, Hincks, magnified. 



Fig. 2. The same, more highly magnified. 



Fig. 3. Lafoea dumosa, Fleming, drawn to the same scale a.s the pre- 

 ceding, to show the comparative size. 



Fig. 4. Calycella obliqua, Hincks, highly magnified. 



Fig. 5. The upper portion of a calycle, to show the structure of the 

 orifice. 



Figs. 6, 7. Lafoea fruticosa, M. Sars, var. gracillima, highly magnified. 

 Drawn from Oban specimens. 



Figs. 8, 9, 10. Lafoea fruticosa, M. Sars, highly magnified. Drawn from 

 Norwegian specimens coumiunicated by Prof. Sars. 



Plate VII. 



Fig. 11. Sertularella pohjzonias, Linnaeus, var. gigantea, magnified. 



Fig. 12. The same, of the ordinary size. Drawn to the same scale for 



comparison. 

 Figs. 13, 14. Sertularella genicidata, Hincks, magnified. 

 Fig. 15. CaU/cella pygm^a, Alder, highly magnified. 

 Fig. 10. Lafoea fruticosa, M. Sars, a slender variety from Shetland, highly 



magnified. 



Plate VHl. 



Figs. 17-20. Calycella quadridentata, Hincks, magnified in different 



degrees. 

 Figs. 21-23. Halecium crenulntum, Hincks, magnified 

 Fig. 24. Calycella syringa, Linn., higlily magnified. 



