Occasional Papers of the Museum of Zoology 57 



30° to that of shell; noticeably flattened on parietal wall; 

 internally light buff to dark chocolate, usually showing the 

 spiral bands when these are present; white peristomal callus 

 often bordered internally by a dark band. Peristome : grad- 

 ually but deeply expanded in palatal and basal portions, and 

 broadly reflected, almost auriculate, in columellar region; 

 parietal angle markedly produced; palatal emargination 

 slight ; internal callus quite thin, but continuous. 



Operculum :^^ about 4 whorls; calcareous pla^^e not exten- 

 sively eroded over nucleus, elsewhere heavy, complete and dis- 

 tant from the horny base; inner surface (horny plate) almost 

 flat; outer surface (calcareous plate) concave at nucleus and 

 with rim of each whorl slightly raised. 



Radula (fig. ix-27) ; C/1 ; L1/1 + 1/5-8; M/56-58. Cen- 

 tral: shaped like a truncated, isosceles triangle; with very 

 heavy base; single cusp stout and heavy; transverse thicken- 

 ing a short distance below cusp. Inner lateral : similar to 

 central but asymmetrical, with inner side longer and heavier 

 than the outer; cusp longer and somewhat more slender. 

 Outer lateral : long, rectangular base, with strong distal reflec- 

 tion, which is pectinated into 5, spatulate, rather indefinite 

 cusps (although 5 is the usual number, interstitial lobes or 

 points may raise the number as high as 8) ; transverse thick- 

 ening prominent, so as to produce a marked angulation on 

 the sides of the base (as seen in profile). Marginal: with 

 numerous, recurved, sharp cusps, which decrease in size 

 towards the outer edge ; the edges of the outer ones pectinate 

 the distal edge of the tooth to fully 1/3 its depth; the un- 

 divided, slightly thickened, recurved, outer portion slopes 

 down abruptly to the comparatively narrow base. 



Measurements 

 Shell Aperture Operculum Whorls 



alt. min.diam. alt. diam. long wide 

 megacheilos P. and M. 

 from text 

 (1838) 15-18 67(10-12) 



39 L. c, fig. ii-10. 



