350 TURRITIDiE. 



Shell small, tapering at both ends, turreted, of a dusky-white or 



slate color ; whorls six, convex, the lowest being half the length of 



the shell, and marked with numerous, slightly elevated, re- 



Fig. 618. yQiyjjjg. lilies, and smaller intervening ones ; about the mid- 



A die is a deep groove, on each side of which is a prominent 



^ revolving ridge or keel, continued upon the upper Avhorls ; 

 p.bkari. lines of growth very minute; aperture elliptical, narrow, 

 ending m a very short canal, inclining a little to the left ; 

 outer lip sharp, toothed by the revolving ribs, with a slight recess 

 or notch at its posterior junction ; pillar lip arched posteriorly. 

 Length, three tenths of an inch ; breadth, three twentieths of an 

 inch ; divergence, forty-eight degrees. 



First found by Mr. Couthouy in a fish caught off Nahant ; since 

 this single specimen, three or four others have been found by Dr. 

 Prescott, of Lynn, and Mr. W. W. Wheildon, of Charlestown. 



This is not likely to be confounded with any other of our shells. 

 Its two revolving ridges mark it well. It is interesting as being the 

 first species of the genus found in our northern Atlantic waters. 

 Neither of our three species belongs, unequivocally, to this genus ; 

 they approach very near to Fksus. Still, the direction of the lines 

 of growth indicate the sinus in the lip to be constant ; and on this 

 their claim to the genus Pleurotoma rests. 



Pleurotoma plicata. 



Fig. 187. 



Shell small, cinereous, ovate; whorls six, reticulated with prominent, longitu- 

 dinal ribs, and elevated, revolving lines ; sinus of the lip distinct. 



Pleurotoma plirata, Adams, Bost. Journ. Nat. Hist. iii. pi. 3, fig. 6. — Gould, Inv. 1st ed. 

 282, fig. 187, — Dk Kay, N. Y. Moll. 150, pi. 6, fig. 120. — Stimpson, Check Lists, 5. 



Shell small, elongated-ovate, somewhat turreted, of an ashy-white 

 color ; whorls six, the lowest one about two thirds the length 

 of the whole shell, and bearing a1)0ut twelve prominent, 

 somewhat oldique, rib-like folds, which are crossed by ten or 

 more elevated, revolving threads, rendering the ribs a little 

 „ , nodulous ; the other whorls form a very pointed, somewhat 

 turreted spire, on which the ribs and revolving lines are con- 

 tinued. Aperture narrow, less than half the length of the shell ; 

 outer lip greatly thickened by one of the ribs, the notch at its pos- 

 terior part being deep, distinct, and smooth. Length, one fourth 



