TROCHUS. 15 



Genus BASILISSA Watson, 1879. 

 Shell conical, carinated, umbilicated, nacreous; last whorl sinua- 

 ted above ; pillar straight, but slightly oblique, thin, hollowed out 

 above, hardly toothed in front, but strongly angulated at base ; 

 mouth rhoniboidal, terminations of peristome not approaching nor 

 connected by a callus. Type, B. lampra Watson. 



N. Pacific 0. 



Genus EUCHELUS Philippi, 1847. 

 Shell globose-turbinate, umbilicate or imperforate; whorls round- 

 ed, spirally granose lirate ; aperture subcircular, outer lip thick, 

 crenulate within, columella with a tooth or a notch at the base ; 

 operculum with few whorls. Type, E. atratus.Gmel. 



Indian and Pacific Oceans. 



Subgenus Olivia Cantraiue, 1835. 



Shell conoidal, imperforate, whorls rounded, cancellated ; apei'ture 



rounded, lirate within, the lip with a strong varix outside ; columella 



sinuous, terminating in a strong truncate tooth at base. Type, O. 



tinei Calc. Mediterranean. 



Subgenus Perrinia H. and A. Adams, 1854. 



Shell trochiform, imperforate, whorls flattened, cancellated ; aper- 

 ture quadrangular, outer lip lirate within, columella short, nearly 

 straight, with several tubercles near the base. Type, P. anguliferus 

 A. Ad. 



The position of this group is problematical. 



Subfamily III, Delphinulin.e. 

 (See Manual of Conchology, x, p. 266.) 



Subfamily IV, IJMBONiiNiE. 



Genus Umbonium Link, 1807. 



Shell with a very thin pearly layer inside, orbicular, depressed, 



imperforated, whorls flattened above, bright, smooth or spirally 



grooved ; aperture wider than high, outer lip thin, acute ; umbilical 



tract covered by a heavy pad of callus. Type, U. vestiarium Linn. 



Indian and Pacific Oceans. 



Genus ETHALIA H. and A. Adams, 1854. 

 Shell orbicular, turbinately depressed ; whorls convex, smooth or 

 transversely striated, the last rounded at the periphery ; umbilicus 



