PTEEOPODOUS MOLLUSCS. 
443 
atl 'l a ventral plate united, with an anterior opening for the head, 
^teral slits for long filiform processes of the mantle, and terminated 
behind in one or three points ; in other cases it is conical or spirally- 
°°iled, and closed by a spiral operculum. The sexes are united, and 
^ J e orifices situated on the right side of the neck. According to 
v °gt 5 the embryo Pteropod has deciduous vola like the sea-snails, 
before the proper locomotive organs are developed.” 
The Pteropods seem to he eminently sociable and gregarious, 
farming together in great numbers ; they present some analogical 
Semblances to the Cephalopoda ; but permanently they represent 
j’he larval stage of the sea-snails. De Blainville divides the group 
lu to two sections, Thecosomata and Gymnosomata, the first including 
^' e Syaloeidse and Lemaoinidte ; the second contains one family, the 
Qtionidm. The Hyalccidse have small horny shells, very thin and 
fr&nsparent, globulous, or elongated, open anteriorly, cloven on the 
i'j 
306 and 307. Hyalea gibbosa (Rang.) Rigs. 308 and 309. Hyalea longirostris (Losuein). 
Sl( fos, and truncate at the posterior extremity. Their globular body 
ls formed of two parts, the one including the head, bearing two very 
'drong tentacles, and two large fins or flappers in the form of wings, 
bringing from each side of the mouth. 
These molluscs are small, and generally of a yellowish-blue or violet 
'-"lour. They are inhabitants of the deep sea, and rarely seen out of 
''hat sailors call ‘‘ blue water.” They plough the waves with great 
j' l pidity by the aid of their formidable fins. Certain winds throw 
h e m sometimes in great numbers on the shores of the Mediterranean. 
lle ®e little creatures, so inoffensive, and which live together in vast 
Ambers, seem to he an easy and ready-prepared prey, which the 
^ l ’ e at marine animals may swallow by thousands. Twenty species of 
hyalea are described as actually living in the Atlantic and Australian 
Seas - Of these Hyalea gibbosa (Figs. 806, 307) and Hyalea longi- 
lo stri s (Figs. 308, 309) are here represented. 
