524 



GASTROPODA. 



[Opisthobranchia . 



Shell spiral, cylindrical or fusiform, external, capable of containing 

 the soft parts ; spire short or sunken and concealed, the apex more or 

 less turned over ; aperture long and narrow, wider below ; columella 

 with a fold or simple ; umbilicus none or very narrow ; operculum 

 wanting. 



KEY TO GENERA. 



A. Shell cylindrical, with conic or flattened spire, the apex pro- 



jecting and mamillar, sinistral, tilted at an angle with the 



body-whorl ; suture channelled ; columella with 1 fold . . TORNATINA. 



B. Shell fusiform, the last whorl forming a projecting process 



above the spire, apical perforation narrow or closed ; 

 aperture as long as the shell, narrow ; columella with no 

 distinct fold . . . . . . . . . . VOLVTJLELLA. 



Genus 1. TORNATINA, A. Adams, 1850. 

 Tornatina, A. Adams, Thes. Conch., ii, 1850, 554. Type : T. valuta, Q. & G. 



Shell cylindrical or oblong, with conical or flattened spire, the 

 apex projecting and mamillar, sinistral, tilted so that its axis lies 

 at an angle of about 90 with that of the shell ; suture channelled ; 

 aperture long, narrow above, dilated and rounded below, the outer 

 lip arched forward, retreating at suture and base ; columella arcuate, 

 calloused, with one spiral fold at its junction with the whorl. 



Distribution. World-wide. These molluscs live at moderate or 

 considerable depths, and probably subsist mainly upon Foraminifera. 

 The species are numerous. 



Fossil in the Cretaceous and Tertiary. 



KEY TO SPECIES. 



A. Shell without microscopic spiral striae. 



a. Columella biplicate ; 1 sharp plait above and 1 rounded 



fold below . . . . . . . . . . biplicata. 



aa. Columella with 1 plait. 



b. Spire raised above the crown, its height about one-fifth 



to one-sixth that of the aperture . . . . Cookiann. 



bb. Nucleus only raised above the crown ; columella with 



1 broad grooved plait . . . . . . Charlottce. 



bbb. Spire not raised above the crown ; columella with an 



indistinct fold . . . . . . . . decapitata. 



B. Shell with more or less distinct microscopic spiral striae. 



a. Columella with a strong plait ; surface with wavy micro- 

 scopic spiral strise . . . . . . . . oruaensis. 



o. Columella with a not prominent fold. 



b. Spire not raised above the crown, involute. 



c. Crown with angularly rounded edge, surface micro- 

 scopically spirally striate . . . . . . Murdochi. 



cc. Crown with carinated and furrowed edge, traces 



of spiral stria? behind outer lip . . . . pach >/<. 



bb. Nucleus raised above the crown, with microscopic spiral 



strise on the lower half of the bodv-whorl tenuilirata. 



