244 MARINE SHELLS 



many fresh water shells, it possesses the power of 

 gliding along the surface of the water, with the shell 

 downward. 



This shell is somewhat like T. reticulata, but the 

 sculpture is less profound, and it has never any ap- 

 pearance of varices, or incrassation of the labrum. 



2. T. *impressa. Shell dusky, acute at the apex : 

 volutions six, with about four acute, impressed re- 

 volving lines ; labrum not thickened, a slight inden- 

 tation at its base, and a projecting angle within on 

 its middle. 



Inhabits the coast of Maryland. 

 Length more than one-eighth of an inch, 

 I have seen but two specimens of this species. 

 The aperture is precisely similar to that of the pre- 

 ceding species. 



3. T. *bisuturalis. Shell thin, pellucid, small, 

 conic ; whirls five, wrinkles almost obsolete, a re- 

 volving impressed line near the suture ; suture not 

 deeply impressed ; spire gradually tapering, rather 

 longer than the aperture ; aperture rounded at base, 

 and perfectly entire. 



Length rather more than one-tenth of an inch. 



Inhabits Boston harbour. 



My cabinet. 



I am indebted to Mr. Aaron Stone, for this small 

 species of Turritella. It is distinguished from all 

 others that I have seen, by the single impressed line. 

 which revolves near the suture. 



