LACUNA. 57 



not only very narrow, but also scarcely raised and very 

 lateral : although much shelving they are rounded. A 

 slight horizontal retusion or flatness under the suture, 

 which is simple, but quite distinct, is principally observ- 

 able upon the body- whorl. This last is remarkably ample, 

 enlarging with great rapidity from the previous turn ; it is 

 much dilated towards the outer margin, is well rounded 

 in the middle, but has its basal surface a little flattened. 

 The apex is small, but not acute. The aperture is more 

 than semicircular, but much longer than it is broad : it is 

 greatly projecting, and very capacious, for it decidedly occu- 

 pies more than one half of the lower superficies of the shell. 

 The outer lip is simply and continuously arched, and dis- 

 posed to expand ; it unites with the inner lip posteriorly 

 at nearly right angles, its anterior junction is devoid of 

 angularity. The general inclination of the white pillar-lip 

 is almost perpendicular, yet slightly retuse : its lacuna or 

 canal is remarkably broad and long, reaching two-thirds up 

 the shell, where it terminates in a large funnel-shaped 

 umbilicus : it is abruptly defined, and almost overhung, as 

 it were, by the body, and although rather profound is not 

 more particularly excavated in the middle than elsewhere. 

 Our larger sjiecimens measured five lines in breadth, and 

 about four lines in length. 



The shell, erroneously called L. patula in our plates, is 

 the immature state of a large olivaceous variety of this spe- 

 cies. Its form is subtriangular, being very broad at the top 

 and attenuated at the basal extremity ; the subsutural canal 

 is peculiarly distinct. The mouth is peculiarly capacious, 

 and is scarcely surmounted by the spire ; it is longer than 

 broad, and somewhat ear-shaped. The chief peculiarity is 

 the entire absence of a lacuna, except when the shell is 

 mature, in which stage of growth it resembles the typical 



VOL. III. 1 



