NATICA. 337 



of the outer one, and is margined with a narrow pallid or 

 whitish strip below the sutural line. The dome-shaped 

 spire is composed of from four to four and a half turns, the 

 lowest of which (the penult volution) is about twice as 

 high as the rest united, and rises somewhat abruptly and 

 ventricosely, but becomes depressed, yet neither flat nor 

 retuse, posteriorly ; the surface of the smaller coils is con- 

 vex, but they are scarcely elevated above the narrow but 

 profoundly impressed subcanaliculated suture. The body, 

 which occupies about five-sevenths of the dorsal length, is 

 simply ventricose, swells out rather abruptly above, is not 

 perceptibly flattened in the middle, and declines at the 

 base in a well rounded but rather rapid fall. The mouth 

 fills about four-sevenths of the ventral length, and about 

 two-fifths of the basal diameter ; it is of a narrow subovate 

 form, being a little more rounded anteriorly, and as usual, 

 is somewhat flattened on the pillar side from the ordi- 

 nary straightness of the inner lip in this genus. The arch 

 of the right lip is not quite semicircular, but it slants at 

 rather an acute angle, as it projects posteriorly from the 

 body- whorl ; its edge is simple and acute. Both the 

 throat and inner lip are quite smooth. The orifice of the 

 umbilicus is intermediate in shape between a crescent and 

 an arrow-head, being contracted by a convex projection of 

 the pillar lip, which is the termination to a rather broad, 

 but little elevated rounded ridge, which winds up the per- 

 foration ; no spiral lines are impressed on its surface, but 

 the corrugations of growth are often very conspicuous. It 

 is sharply defined anteriorly, where it indents the pillar ; 

 the adjacent area is a little flattened, but is not bounded 

 by a distinct further angulation. The white enamel is not 

 much spread upon the body. The operculum is dirty 

 yellow. Our largest examples measure but little more 



VOL. TII. ■ X X 



