382 PTEROPODA. 



SPIRIALIS. Eydoux and Souleyet. 



Shell thin, transparent, of several spiral whorls, coiled 

 sinistrally, spire elevated or depressed, surface smooth or 

 (in some foreign species) reticulated, mouth angulated be- 

 low or canaliculated, sometimes prolonged into a spine-like 

 curved beak. 



Animal elongated spiral, head not distinct ; two fin-like 

 expansions united at their base by an intermediate lobe 

 bearing an operculum ; branchiae in a cavity formed by the 

 mantle. Operculum vitreous, very thin and transparent, 

 of few whorls. 



This genus was constituted in 1840 * by the naturalists 

 attached to the exploring ship Bonite, for some curious 

 minute oceanic Pteropods with which they had met during 

 their voyage. They were the first to meet with and de- 

 scribe the animal inhabitants of certain little sinistral fusi- 

 form shells, which had been placed in Atlanta by Alcide 

 d'Orbigny, but which had evidently no affinity with the 

 Nucleohranchiata. Long before, one of these from Rimini 

 in Italy had attracted the notice of Spengler and been 

 figured by Chemnitz, -f- and another had been described and 

 figured as a reversed form of Fusus by Dr. Fleming. In 

 1842 one of the authors of this work founded a genus under 

 the name of Peracle for a remarkable minute shell dredged 

 at great depths in the ^gean, and at the Cork meeting of 

 the British Association referred Dr. Fleming''s Fusus retro- 

 versus to the same genus, giving reasons why they should 

 be considered Pteropods, unaware of their true position in 

 that group having been already discovered and published 

 by the French naturalists already cited. About the same 



* Revue Zoologique Soc. Ciiv. Io40, p. 235. 

 t Cliemnitz, Conch. Cab. vol. ix. pi, 113. 



