MEDUSJE. I. 95 



further development there is a well marked difference between the sexes, the gonads being distinctly 

 longer in the males than in females of corresponding sizes. The difference is so obvious that it can 

 hardly be due to casuality. We may state, in short, that in full-grown specimens the male gonads are 

 about 2 /3 r, the female gonads about l / 2 r. In large specimens the gonads, particularly the male 

 gonads, are more or less sinuous. 



Occurrence: The medusa Phialidium hemispharicum is very abundant round the British 

 coasts, in the North Sea, and in the Danish waters to the western part of the Baltic. Within this 

 region it is found throughout the year. Young specimens are found in the spring and summer; during 

 the summer we also find half-grown specimens; during the autumn and far into the winter we find 

 large, full-grown specimens. The medusa has also been found at the coast of Norway in the neigh- 

 bourhood of Bergen. Among the material, here dealt with, there are a number of small specimens from 

 the Faeroe Islands, found in August, and numerous large individuals from the south coast of Iceland 

 from July and August. - - If Mayer (1910) is right that the "Clytia flamdula" of Metschnikoff is 

 identical with Phialidium hemispharicttm, we will have to add the Mediterranean to the known area 

 of distribution of the species. 



Phialidium islandicum nov. spec. 



Plate IV, figs, n, 12, 13; Plate V, figs, i and 2. 



Diagnosis: Phialidirim of large size, with elongated gonads, with numerous tentacles and 

 an equal number of marginal vesicles. 



Description: Umbrella is watchglass-shaped, about 35 40 mm in diameter, gelatinous sub- 

 stance comparatively thin, exumbrella evenly rounded from the apex towards the margin. The stomach 

 is cross-shaped, very small, its perradial diameter being only about one-tenth the diameter of the bell. 

 There is a short mouth-tube provided with four pointed, crenulated lips (Plate IV, fig. 12). Four radial 

 canals, straight and narrow, and a narrow, simple circular vessel. The gonads are developed on the 

 radial canals, completely encircling the canal from both sides of its line of attachment to the subum- 

 brella without leaving a ventral line free of gonads. The gonads are very much elongated, linear, 

 usually not sinuous (Plate IV, fig. u), commencing about 2 mm from the base of the manubrium, 

 terminating about i mm from the circular vessel. The number of tentacles amounts to about 200; their 

 basal bulbs are swollen (Plate V, fig. i), particularly owing to the ectoderm of the lateral sides being 

 highly developed; there is a slight trace of an abaxial process at the base of the tentacles. There are 

 no cirri. Small, closed marginal vesicles (Plate IV, fig. 13) are present in the same number as the tent- 

 acles. Velum is fairly broad but thin and weak. -- Hydroid generation unknown. 



The number of species of Phialidium hitherto described is very large, and several of the species 

 are very much like each other. It might be considered as rather a risky undertaking, therefore, to add 

 a new species to the number already described, but as far as I am aware, there has never been found 

 a Phialidium of such considerable size and with a similarly great number of tentacles as that found 

 in the present species. It was pointed out in the preceding pages that Phialidium hemisphcericum 

 may attain a larger size and a larger number of tentacles in the waters near Iceland than in the more 



