SECT. in. THE PORPITA. 117 



youngest form yet discovered is that described by Prof. 

 Huxley, in his excellent monograph on 'Oceanic Hy- 

 drozoa.' 8 The Velellidse are inhabitants of warm and 

 tropical seas, but are occasionally found on the coasts 

 of Great Britain, being carried by the Gulf Stream to 

 the Bay of Biscay, and thence wafted northwards by 

 the prevalent winds. 



Although the Porpita, a genus of the Velellidse, has no 

 sail, it is akin to the Velellse in size and structure. The 

 body of the Porpita consists of two circular cartilaginous 

 disks, united at their edges and surrounded by a blue 

 membranous limb. On the surface of the upper disk 

 there are beautifully radiating striae, each of which ends 

 at the circumference of the disk in a little protuberance, 

 which gives it the appearance of a toothed wheel. A 

 large sterile polypite occupies the centre of the under- 

 surface of the body, surrounded by a zone full of 

 smaller ones ; and the space between the zone and the 

 blue limb is occupied by a narrow area of a reticulated 

 appearance, to which numerous circles of tentacles 

 are fixed, that spread out and radiate all around the 

 margin of the animal. The interior circular rows are 

 simple, short, and fleshy, not extending much beyond 

 the edge of the limb : the succeeding circles are gra- 

 dually longer, while the exterior row, which extends far 

 beyond the limb, are branched and beset with slender 

 filaments, ending in minute globes, sometimes filled 

 with air, so that a Porpita is like a floating daisy, 

 though differently coloured. The Porpita glandifera, a 

 pretty little inhabitant of the Mediterranean, which 

 only appears in calm weather, is not more than eight 

 lines in diameter ; somewhat convex, white, marked by 

 radiating striae, and encompassed by a dark blue limb. 

 The central polypite and those next to it are whitish, 



* Published in 1858, by the Ray Society. 



