SIMPLICIA. 511 



and dilatations assist the locomotion of the animal. The edges of this um- 

 bella, as well as the mouth, or the suckers more or less prolonged into 

 pedicles which supply the want of it, in tlie middle of the inferior surface, 

 are furnished witli tentacula of various forms and very different sizes. 

 These various degrees of complication have given rise to numerous divisions. 



The two following genera, which were formerly joined with the 

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

 count of the internal cartilage which supports the gelatinous sub- 

 stance of the body. 



PoKPiTA, Lam. 



Where this cartilage is circular and its surface marked with concentric 

 strise crossed by radiating striae. The superior surface is merely invested 

 with a thin membrane that projects beyond it; the infei'ior is covered with 

 a great number of tentacula, the exterior of which are the longest, and fur- 

 nished with little ciha, each terminated 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 sa- 

 lient proboscis. It leads to a simple stomach surrounded by a sort of glan- 

 dular 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 exterior of which 

 is the longest, but the latter are not ciliated, and a still more important 

 character is, that tlie cai'tilage, which is oval, has on its superior surface a 

 vertical and tolerably elevated crest. This cartilage is diaphanous, and is 

 merely marked with concentric striee. A species of this genus also is known, 

 of the same colour as the Porpita and inhabiting the same seas. It is eaten 

 fried. 



ORDER II. 



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 



