SIMPLICIA. SY 
in radii on its-convexity. This species also is extremely com- 
mon, and varies greatly as to the spots(1). 
We have given the general name of Ruizostoma to that portion 
of the great genus Medusa which comprises species that have no 
mouth opening in the centre, and that appear to live by the suction 
exercised by their pedicles or tentacula. They have four or more 
ovaries. 
RuIzOSTOMA, proper, 
Includes those which are furnished with a central pedicle more or 
less ramified according to the species. 
The vessels arising from the small ramifications of the pedicles 
unite in a cavity of its base, whence branches proceed to all parts of 
the umbella. 
The most common species is the Rhizostome bleu, Cuv., Journ. 
de Phys., XLIX, p. 436; Réaum., Ac. des Sc., 1710, pl. XI, f. 
27,28. Itis found along the French coast at low water, and 
its umbella is sometimes almost two feet in width. Its pedicle 
is divided into four pairs of arms almost infinitely forked and 
dentated, each one being furnished at base with two auricles 
that are also dentated; a fine network of vessels extends round 
the umbella in the thickness of its margin(2). 
(1) Most of the Chrysaora of Péron are mere varieties of this species—Add 
Aurelia crenata, Chamiss., and Eisenh., Ac. Nat. Cur., X., p. I, pl. xxix. 
Besides the Chrysaora, we refer to this genus the Aurrria, Cyanra, OBELIA 
and Ocranta of Péron: we also include in it Medusa hemispherica, Miill., VII, 5; 
Encyc., 93, 8, 11;—M. cymbaloides, Slaber., Encyc., Ib., 2—4, if we may trust to 
the characters of such small individuals;—Callirhoe basteriana, Pér.; Baster, Op. 
Subs., II, v, 2, 3; Encyc., XCIV, ‘4, 5;—the Cyanée bleu, Pév.; Diquemare, Journ. 
de Phys., 1784, Dec. I;—the species or varieties figured, but rudely, by Borlasse, 
Nat. Hist. of Cornw., pl. xxv, f. 7—12, which are referable to our Chrysaora, 
and to which should be approximated the Med. hysocella, Gm. ;—. tyrrhena, 
Gm., &c. 
(2) It is the Pulmo marinus, Mathiol., Aldrov., Zooph., lib., IV, p. 575, the 
Medusa pulmo, Gm., Macri, Polm. Mar., I, B; Borlasse, XXV, 15. See Eisenh., 
Ac. Nat. Cur., X, part Il, p. 377. 
The Potta marina, Aldrov., Ib., p. 576, is perhaps another species. 
I suspect that the Ernira, Pér.,—WMedusa simplex, Pennant; Borlasse, Cornw., 
XXV, 13, 14—is merely a Rhizostoma deprived of its pedicle. 
The Medusa pileata, Forsk., of which Péron makes an Oceania, has the ramous 
pedicle of Rhizostoma proper, but enclosed under a campanulate umbella, fur- 
nished at the margin with tentacula. 
Vout. I1V.—2 X 
