44 



islands/' writes Professor Edward Forbes,* who had frequent opportunities 

 of observing the Pteropods of the Mediterranean and ^Egean Seas, " the 

 surface of the water, when the weather is calm and the sun is shining, 

 glistens with glassy needles or shelly bubbles. These, upon closer exami- 

 nation, prove to belong to curious mollusks, which instead of creeping 

 over submarine rocks and weeds, or burying in the soft mud and sand of 

 the sea-bed, aspire to a gayer and more sportive life, and play the part of 

 Neptune's bees and butterflies.'" According to the observations of M. 

 IVOrbiguy, the Pteropods begin to appear at twilight, and particular spe- 

 cies rise to the surface at successive hours of the night. He considers 

 that they inhabit particular zones at different depths, and occupy as many 

 periods of time in making their way to the surface, disappearing again at 

 the approach of day. It would appear from the remarks of Edward Forbes 

 and D'Orbigny that their observations are at variance ; but it is more than 

 probable there are day Pteropods as well as night Pteropods, and that, 

 like the travellers who differed on the colour of the chameleon, both are 

 equally right. t 



The Pteropods are only known to the conchologist by a few little glassy 

 shells, of which it is scarcely necessary to particularize the species. The 

 largest are those of Hyalcea and Cleodora, with shells of a globose form, 

 armed with cusps or elongated spines. Cuvieria has a small cylindrical 

 shell; in Creseis it is needle-like; and in Atlanta it has the discoidal form 

 of a Nautilus. 



Class 4. LAMELLIBRANCHIATA. 



Animal ; body a mass of viscera furnished on each side with two 

 lamella-like bronchia, and enveloped by a sac or mantle, which 

 secretes on either side a shelly valve, connected at the dorsal 

 margin by an clastic horny ligament; no distinct head or eyes ; 

 month represented by a simple opening in the front part of the 

 mantle ; hind part of the mantle opened, with the edges some- 



* Brit. Moll. vol. ii. p. 377. 



f Dr. Johnston gives a most picturesque account of the upward flight of the Cleodores, "when 

 the garish eye of day begins to dawn," and of the gradual appearance of the Ilyahs, "who do 

 not leave the abyss and mingle in the crowd until night lends them her friendly veil."' Mr. 

 Godwin-Austen's humour is of a rougher kind. In his continuation of Forbes' ' Natural History 

 of the European Seas,' the Pteropods are described as leading a life of dissipation. The sun- 

 delighting bees and butterflies of the iEgeau, whose characters have been hitherto irreproachable, 

 are likened to gnats and moths who " shim the light, aud if the sun is bright you may look in 

 vain for them during the live-long day. HyaUea tridentata, though it does not venture out till 

 dusk, retires early, whilst some spe. ies. such as Cleodora pyramidata, are to be met with only 

 during the midnight hours and the darkest nights. This tribe, like a higher one, has its few 

 irregular spirits who manage to keep it up the whole night through. All, however, are hack to 

 their homes before dawn surprises them."' 



