502 RADIATA. ACALEPHA. Rhizostoma. 



M. cap. Bast. Op. ii. 60. t v. f. 1. Turt. Brit. Fauna, 139. StewarCs 

 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. 



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

 eight arms. 



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

 tipped with blue. 



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

 of Cornwall. 



On the oral disc there ai*e 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. ovatus. — 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, Flem. 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 ojiening 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. 



