368 Description of some New Shells. 



Greatest length, viz. from beak to posterior-ba- ") ^ ,g #. . * 

 sal margin, 



Greatest breadth at right angles to the above line, 0*35 " 



Diameter " " " " 0-25 " 



Inhabits Provincetown harbor, (Mass.) • 



This very pretty Modiola I have found only at the above place. 



The form is remarkable for the genus, being almost truly oval, 

 and quite regularly convex. In the smaller specimens the umbones 

 are, however, sometimes more prominent. The above dimensions 

 are of the largest specimen I have seen. 



Genus Acteon, Montfort. 



A. trifidus. 



Fig. 4. — a, enlarged — J, natural size. 



Shell small, acute-conic, glossy-white, pellucid: whirls about eight, 

 flat, with about six impressed revolving lines, the one immediately 

 above and the two next below the suture, wider, deeper, and distinct, 

 the intermediate lines, and also about twelve on the lower portion of 

 the body-whirl, generally obsolete; transverse striae obsolete : spire 

 gradually tapering to an acute apex: suture proper not impressed : 

 mouth elongate, one third the length of the shell, acutely angular 

 above, produced and rapidly rounded below, base not effuse : colu- 

 mella-edge slightly recurved below: columella with one oblique fold : 

 outer lip entire, not thickened and sometimes showing within, and 

 on its sharp edge, the impressed lines : operculum horny. 



Length, 0.20 of an inch. 



Greatest breadth, 0.08 do. 



Inhabits the shores of Rhode Island. Found adhering to Pecten 

 concentricus. 



Genus Turbo, Lin. 

 T. inflatus. 



Fig. 5. — a and 6, enlarged — c, natural size. 

 Shell small, sub-globular, umbilicated, thin, shining, translucent : 

 whirls five, convex, obsoletely and transversely striate, and furnished 

 with a few obsolete revolving lines on the lower side of the body- 

 whirl : spire low, convex, obtuse, shorter than the aperture : suture 

 a little impressed : mouth round : outer lip sharp : color pale brown- 

 ish-yellow, or horn color, immaculate : operculum round, horny, 

 inultispirate. 



Length, 0.19 of an inch. 



Greatest breadth, 0.23 do. 



