PTEROCERAS 



TESTA subturrita, ovato-oblonga, subventricosa, 

 anfractu ultimo majore, basi in canalem elonga- 

 tum, plerumque reciirvum desinens. •Apertura 

 oblonga, in canalem, interdum duplicatum su- 

 perne extensa. Labium externum aetate dila- 

 tatum, in alam digitatam, inferne lacuna in- 

 terruptam distinctum. Operculum corneum, 

 crassum, oblongum, basi acutum. 



Distinguished from Rostellaria, as we have shown before, 

 by the position of the sinus near the base of the outer 

 lip ; also by its short spire, and its outer lip being di- 

 vided into variously curved digitations ; this latter cha- 

 racter, joined to its elongated, generally curved canal at 

 the base, will serve also to distinguish it from Strombus. 



Shell ovately oblong, rather ventricose, turrited, 

 spire short, with the last volution very large, and its base 

 generally produced into an elongated, mostly recurved 

 pointed canal. Aperture oblong, its upper extremity 

 extended into a sometimes double canal. Outer lip thin 

 and sharp edged when young; but when full grown, 

 thickened, and expanded into the form of a wing, divided 

 into several horns or digitations, whence the name 

 Pteroceras, and having a strongly marked sinus near the 

 lower part, but not close to the base. 



Operculum horny, thick, oblong, rounded at the 

 upper part, by which alone it is attached to the foot of 

 the animal, and pointed at the lower end, exactly like 

 that of Strombus. 



Lamarck describes only seven species of Pterocerata, 

 all of which are recent; nor have we ever seen any fossil 



