HETEROFUSUS. 59 



Ex. L. arctica, 0. Fabricius, pi. 7, fig. 3. Shell, L. 

 arctica, fig. 3, a. 



The only species of this genus known, L. arctica, ac- 

 cording to Scoresby, is extremely abundant in the North 

 Seas, but rarely met with out of sight of land ; it forms 

 an important item in the diet of the whale. The operculum, 

 if it exists in this genus, has not yet been observed. 



Genus SPIRIALIS, Eydoux and Souleyet. 



Shell thin, vitreous, discoidal, depressed, sinistral ; axis 

 umbilicated ; whorls smooth ; aperture angiilated below or 

 canaliculated, sometimes prolonged into a spine-like curved 



beak. 



Operculum glossy, thin, transparent, of few whorls, with 

 a central muscular scar. 



S^n. Heliconoides. D'Orb. 



Ex. S. veutricosa, Eydoux and Souleyet, pi. 7, fig. 4. 

 Operculum, S. ventricosa, fig. 4, a. Shell, S. rotunda, 

 UOrhigny, fig. 4, h. 



Although this genus reminds one very forcibly of the 

 larval form of the Gasteropods, it is, from the animal, a 

 true Pteropod; it may be known from the shell of the very 

 young Atlanta and Garinaria by being sinistral. 



Species of Spinalis. 



australis, Eyd. and Soul. rotunda, DVrh. 



inflata, D'Orb. ventricosa, E^/d. and Soul. 



JeiFreysii, Forbes andHanley. 



Genus HETEROFUSUS, Fleming. 

 Shell thin, transparent, sinistral, conical, turreted ; spire 



