502 RADIATA. ACALEPHA. Rhizostoma. 



M. cap. Bast. Op. ii. 60. t. v. f. 1. Turt. Brit. Fauna, 139. Stewart's 

 El. i. 399. — Not uncommon. 

 Colour brownish, with a central mark, from which 16 rays diverge ; oral 

 disc with numerous capillary filaments. 



Gen. XXIII. RHIZOSTOMA.— Four cavities beneath, with 

 a central peduncle divided into arms. 



63. R. undulata. — Circumference waved, with fangs in the 

 projecting parts. 



Borl. Corn. 257, t.xxv. f. 15 M. und. Penn. Brit. Zool. iv. 58 — Shores 



of Cornwall. 

 Margin thin ; peduncle divided into eight arms, with a pair of lobes at the 

 base of each. 



Gem. XXIV. CASSIOPEA.— Eight cavities beneath, with 

 eight arms. 



64. C. lunulata. — Margin with numerous semicircular fangs 

 tipped with blue. 



Borl Corn. 258, t. xxv. f. 16 M. lun. Penn. Brit. Zool. iv. 58.— Shores 



of Cornwall. 

 On the oral disc there are eight semicircular openings, with eight arms 

 having jagged edges, and sixteen jagged processes at the base. 



The characters of the preceding species of the Linnean genus Medusa, re- 

 quire revision, and the species should be studied with reference to the 

 changes in form which they experience by age. The Medusa simplex of Pen- 

 nant and M. scintillans of Macartney, are probably the fry of some of the es- 

 tablished species. 



Gen. XXV. BEROE.— Body with vertical ciliated ribs; tu- 

 bular vessels traverse the axis of the body, with lateral and 

 terminal apertures. 



65. B. ovuhis. — The body orbicular, slightly depressed at 

 the summit, and a little protuberant at the base. 



Bast. Op. i. 123, t. xiv. f. 5 B. infundibulum, Fab. Fauna Groen. 360.— 



Beroe, \F/o». Wern. Mem. iii. 401, t. xviii. f. 3, 4 — Frith of Tay. 



The following observations were made from an inspection of the only spe- 

 cimen of this animal which I have had an opportunity of seeing : " There 

 were eight vertical bands or ribs, extending from the summit to the base. 

 These were narrow, denticulated on the margin, confined to the surface, and 

 of a denser substance than the gelatinous interior. From the central sur- 

 face of the ribs, a number of filaments proceeded, which were lost in the sub- 

 stance of the body. The mouth, or the opening at the base, had some ap- 

 pearance of having its margin divided into four lobes. The tube which con- 

 ducts from the mouth to the centre of the body, and is prolonged in its axis 

 to the summit, had on each side a compressed organ adhering to its walls. 



