MEDUSA. I. 



vessel. About 32 fairly long tentacles. 8 marginal vesicles, each containing 3- 4 or more concretions. Velum well developed. 

 Manubrium, gonads, and tentacular bulbs yellowish or reddish-brown. 



This diagnosis is based on specimens, examined by me at Plymouth, and it differs in certain regards from that given 

 by Mayer. 



The corresponding hydroid is Campanulina repens Hincks. 



The medusa is common off the coasts of Great Britain and Holland 



Genus Phialidium Leuckart. 

 Phialidium hemisphsericum (Gronovius). 



Plate IV, fig. 14; Plaje V, fig. 3. Textfigs. 16 and 17. 



Medusa hemispharica Gronovius 1760. Observationes de animalculis . . . Acta Helvetica. Vol. IV. p. 35. 

 Thaumantias hemisph&rica Forbes 1848. British Naked-eyed Medusae. p. 49. 

 i. p. Phialidium variabile Haeckel 1879. System der Medusen. - - p. 186. 



Pln'alidinin temporarium Browne 1896. On British Hydroids and Medusae. Proceed. Zool. Soc. Lon- 

 don. - - p. 489. Plate XVII, figs. 4, 5, 6. 

 hemispharicum Mayer 1910. Medusae of the World. p. 266. 



For further synonymy, see Browne 1896 and Mayer 1910. 



Bell nearly hemispherical, 20 25 mm wide; gelatinous substance thin. Manubrium small, with 

 4 simple lips. 4 slender radial canals. Gonads oval or linear, their length very much varying; they are 

 placed along the radial canals, somewhat nearer to the circular vessel than to the manubrium. 3058 

 long tentacles with somewhat swollen basal bulbs. Usually 2 marginal vesicles between every succes- 

 sive pair of tentacles, each vesicle containing one concretion. Velum fairly narrow. Stomach, gonads, 

 and tentacular bulbs yellowish-brown or reddish-brown. 



Among the numerous species of Phialidium described, two species are recorded as occurring in 

 the North-Atlantic area, viz. Phialidium hemisph&ricum (Gronovius), about 20 mm in diameter, with 

 up to 39 tentacles (according to Browne; as to the Icelandic specimens, see below), usually with 2 

 marginal vesicles between every successive pair of tentacles, and with linear, elongate gonads on the 

 outer halves of the radial canals; and Phialidium buskianum (Gosse) Browne, up to 6 mm in diameter, 

 with 20 32 tentacles, with one, sometimes 2, marginal vesicles between every, successive pair of tent- 

 acles, and with short, oval gonads between the middle of the radial canals and the circular vessel. 



I am very much inclined to think that these two species cannot be kept apart. But the North- 

 Atlantic material at my disposal cannot serve as foundation for a discussion of the matter. The Zoo- 

 logical Museum of Copenhagen possesses, however, a very large material of Phialidintn from the 

 Danish waters and, moreover, a great many specimens, which I brought home from Plymouth in 1914. 

 I consider it most convenient, therefore, to postpone a thorough discussion of the variation of Phiali- 

 dium and the question of the limitation of the species, until that material lias been further examined. 

 In the present paper I shall restrict myself to give some information concerning the present 

 material. 



