OLIVANCILLAIUA. 141 



truncate posteriorly, shield with the side-lobes very large 

 and rounded. 



Operculum distinct, half-ovate, nucleus subapical. 



Shell smooth, oblong ; spire short, suture not canali- 

 culated to the apex ; aperture moderate ; columella with 

 two or three oblique plaits anteriorly, and with a large 

 callosity posteriorly. 



Ex. O. vesica, Gmelin^ pi. 15, fig. 2. Shell, O. vesica, 

 fig. 2, a. 



In this genus the suture of the spire is usually filled up 

 with a callous deposit, and the spire is often very short. 

 In the animal the hind part of the mantle ends in a large, 

 thick, fleshy process, which partly covers the spire. 



Species of Olivancillaria, 

 Braziliensis, Chem. 



Sub-gen. utriculina, Gray. 



Spire acuminated, suture channelled as far as the apex ; aper- 

 ture moderate ; last whorl simple. 



acuminata, Lam. ligneola, Reeve. 



ancillaroides, Reeve. lutaria, Bolt. 



gibbosa, Born. nebulosa, Latn. 

 litterata, Lam. 



Sub-gen. lintricula, H. aud A. Adams (Scaphula, Sivainson, 



not Benson). 

 Shell oblong, ventricose, thick ; spire very short, obtuse, cal- 

 lous, suture not channelled to the apex ; aperture very wide. 



aquatilis, Reeve. vesica, Gmel. 



