32 



The Shell is imtransparent, or opaque, of white color, and usually quite smooth, with- 

 out visible longitudinal stripes or ribs. It resembles therefore in this respect more the D. 

 entalis, from which it is however at once distinguished, as well by its slender and elongated 

 shape, as by its duller and less lustrous surface. We observe on it, as on that of the D. 

 entalis, evident lines of growth, which are circular or somewhat oblique, parallel with the 

 anterior edge, and which at certain intervals are more distinctly marked, and sometimes even 

 form thickened places on the shell, by which its outlines may often be rendered a little irre- 

 gular. In the posterior third part, the shell assumes nearly always (see fig. 4. 6. 10) a darker 

 dirty-grey color; and on examining this part with the microscope, we perceive that the appear- 

 ance is produced chiefly by peculiar ramified superficial marks, composed of numerous raised 

 lines, anastomosing with each other in various manners, and forming, especially towards the 

 anterior part, (fig. 9.), an extremely fine net. Nearer the apex (see fig. 7. & 8.) the lines 

 become less fine and less close, taking more the form of branched tubes. It appears however 

 that this is not, as I was at first inclined to presume, something originally belonging to the 

 shell, but an extraneous body; because we find shells^on which this peculiar reticulation is 

 entirely wanting. I have in vain endeavored to discover the origin of this extraordinary 

 ' ramified marking, which, as I have subsequently ascertained, is not only not restricted to this 

 species, but has also been formerly mentioned by Jeffreys, as observed in very different mol- 

 luscs (Littorina). Probably it is one of those (as yet little known) lower organisms, concerning 



