PHASIS. 37 



lip thin, simple, its eolumellar margin dilated. Type H. menkeana 

 Pfr., pi. 10, figs. 1, 2, 3. 



Distribution, South Africa. 



Uuder this genus as subgenera may be ranged two groups : Tra- 

 chyeystis and Seulptaria, both belonging to the S. African fauna. The 

 anatomy of typical Phasis is unknown. That of Trachycystis is 

 described below. The diagnosis given above applies to the restricted 

 subgenus Phasis only, to which the following species belong : 

 P. capensis Pfr. iii, 103. P. namaquana Mts. viii, 297. 



irrorata Zieg. P. paludicola Bens, iii, 104. 



littorieola Bens. P. sturmiana Pfr. vi, 317. 



P. menkeana Pfr. iii, 108. P. uitenhagensis Kr. iii, 104. 



Subgenus TRACHYCYSTIS Pilsbry, 1892. 



Trachycystis PILS., Man. of Conch, viii, p. 136. Pella Alb. (in 

 part), Die Hel. (2), p. 84, 1860. Not Pella Steph. 1832. 



Shell small, thin f generally somewhat translucent, horny or earthy 

 brown in color, usually sculptured with oblique riblets or rib-striae, 

 the apical whorl spirally striated (fig. 7) ; aperture lunate ; lip 

 simple, thin, dilated at the eolumellar insertion. Type P. biseulpta 

 Bens., pi. 10, figs. 5, 6, 7 ; see also P. browningi Bens. pi. 10, 

 figs. 8, 9. 



Animal (of P. rariplieata) having a rather long slender foot, the 

 sole apparently undivided ; foot-margins wide, not crenulated nor 

 more coarsely granulated than the rest of the surface, defined by a 

 pair of shallow grooves; tail lacking a mucous pore. 



Jaw thin, having numerous flat plaits. 



Radula having the transverse rows of teeth crowded, so that the 

 cusps of one row project over the bases of the next. Central teeth 

 tricuspid, the mesocone longer than the basal plate, slender, side cusps 

 small. Lateral teeth altogether similar, but slightly asymmetrical, 

 the entocones increasing in length outwardly. Transition from 

 lateral to marginal teeth very gradual, the latter tricuspid, the 

 ento- and mesocones subequal, long, oblique and united at their 

 bases, the ectocone smaller, simple (in P. biseulpta) or bifid (P. rari- 

 plicata}. PI. 15, figs. 3, 4, P. biseulpta. 



All of the teeth are tricuspid ; the,'central and inner lateral teeth 

 are so similar that it is difficult to distinguish which is the rhachi- 

 dian row, and the mesocones are long and slender. The inner mar- 

 ginal teeth are remarkable for their long ento- and mesocones. 



