MOLLUSCA. 315 



smooth blue membrane, whilst its lower is provided 

 with a mat of blue tubular papilla and some marginal 

 cilia, and has a central alimentary tube. 



One species we observed is about the size of a 

 six-pence ; the upper surface of its fulcrum is uniformly 

 marked with concentric circles, and has a projecting 

 tubercle in its centre, from which numerous raised lines 

 radiate to the circumference the whole bearing some 

 resemblance to a fe worked" shirt-button. 



A second species (P. Gigantea ?) is the size of a 

 half-crown, and has the upper surface of its fulcrum 

 muricated, or studded with rough tubercles. The 

 papillous appendages on the lower surface of this, 

 as well as of the former species, appear to possess a 

 strong sucking power ; for, when placed on the 

 finger, they adhere so firmly to it, as to separate from 

 the animal by the force required to detach them. 

 Like Velella, they do not move when captured the 

 layers of their fulcrum contain fixed air and their 

 bare skeletons are often found floating on the sea. 



Specimens of both the above species were taken in 

 the Pacific, from lat. 30 N. to 9 S. 



THE SEA LIZARD. 

 (Glaucus Hexapterygius, Cuv.) 



This curious mollusc occurred to us near the Equator, 

 in long 22 W., and as high as the thirtieth parallel of 

 north and south latitude, both in the Atlantic and 

 Pacific Oceans. Examples were captured only during 

 a calm, and when the sea was particularly smooth, and 

 their number at these times appeared to be great beyond 

 all reasonable conception. 



The average length of the species is about an inch- 

 and-a-half ; and its form fully justifies the trivial name 



