HYDROSTATICA. 427 



Medusae might also constitute a small family in this order, on account 

 of the internal cartilage which supports the gelatinous substance of 

 the body. 



PoRPiTA, Lam., 

 Where this cartilage is circular, and its surface marked Avith con- 

 centric striae crossed by radiating strife. The superior surface is 

 merely invested with a thin membrane that projects beyond it; the 

 inferior is covered with a great number of tentacula, the exterior 

 of which are the longest, and furnished with little cilia each termi- 

 nated by a globule. They sometimes contain air ; those in the 

 middle are the shortest, simplest and most fleshy. In the centre of 

 all these tentacula is the mouth, in the form of a little salient pro- 

 boscis. It leads to a simple stomach surrounded by a sort of glandular 

 substance. 



One species is known of a beautiful blue colour, that inhabits 

 the Mediterranean, and seas of hot climates*. 



Velella, Lam., 

 Where, as in Porpita, there is a mouth in the inferior surface in the 

 form of a proboscis, surrounded with innumerable tentacula, the ex- 

 terior of which is the longest, but the latter are not ciliated, and a 

 still more important character is, that the cartilage, which is oval, 

 has on its superior surface a vertical and tolerably elevated crest. 

 This cartilage is diaphanous, and is merely marked with concentric 

 striae. 



A species of this genus also is known, of the same colour as 

 the Porpita, and inhabiting the same seas. It is eaten fried f . 



ORDER 11. 



HYDROSTATICA. 



The Hydrostatic Acalepha are known by one or more bladders 

 usually filled with air, by means of which they suspend themselves in 

 their liquid element. Excessively numerous and variously shaped 

 appendages, some of which probably serve as suckers, and the others 



* It is the Med. umbella. Mull., Natur. of Bed., Besch., II, ix, 2, 3; Hohfhuria 

 nuda, Gm.; Forsk., XX\' I, 1, i ; and Eacyc, XC, 6, 7; Purpita yiyantea, P^r., 

 Voy., XXXI, G. 



The Medusa porpita, L., is merely its cartilage divested of the gelatine and ten- 

 tacula. 



The Porpite appendicuUe, Bosc, Vers, II. xviii, 5, 6, if not an altered individual of 

 the same, should constitute a separate subgenus. It is the genus Polybrachi- 

 ONiA, Guilding., Zool. Journ., XI. 



t It is the Medusa velelta and the Holofhuria spirois, Gm.; Forsk., XXVI, k; 

 Encyc, XC, 1, 2. The Velella scaphidia, Per. Voy., XXX. 6, is nowise generically 

 different ; it appears that there are several species, such as the V. oUonga, V, 

 sinistra, V. lata, Chamiss. and Eisenh., Ac. Cur. Nat., X, p. I, pi. xxxii. 



ff2 



