6O UNIVALVES. 



In the remainder of our shells the lip is not turned inwards. 

 Three of the genera are spindle-shaped, and have a long, narrow 

 mouth. In one the mouth is smooth, in another it is grooved, in 

 the other it is ridged. In the first the outer lip is notched, in the 

 last it is curved. This will serve to distinguish them, thus : 



Mouth smooth, outer lip notched in the middle Pleurotoma. 

 Mouth grooved, outer lip notched at top Mangilia. 

 Mouth ridged, outer lip curved Lachesis. 



In this triad, the slit in the mouth ought to mark off the two first at 

 once, but the writer has not been fortunate enough to find it always 

 in Mangilia, and only once or twice in Pleurotoma', doubtless it was 

 there, but it was too faint to talk about, in some specimens at all 

 events. In Mangilia it comes just where the lip joins the periphery. 

 In both genera, as usually figured, it is unmistakable. Lachesis has 

 a shorter mouth than the other two, and is a heavier, clumsier sort 

 of shell about the same size, easily distinguished from the others by 

 its thick mouth. Mangilia, it may be as well to say, is quite as well 

 known as Defrancia, and is as often 'spelt Mangelia, a name which 

 was at one time applied to Pleurotoma. 



In our next two groups the month is broken by a long notch, 

 which may be called a canal. In some cases this canal is curved, 

 in others it is straight. It is curved in four genera, Columbella, 

 Nassa, Buccinum, and Buccinopsis. Of these the first can be 

 recognised by the fold at the base of the pillar, and by the curious 

 projection of the outer lip alongside the notch. Nassa has the 

 curvature of the canal distinctly shown, and has a characteristic 

 tooth or teeth at the base of the pillar. In the other two genera the 

 pillar is smooth, the difference being that in one, Buccinum, the 

 whelk, the shell is coarsely ribbed ; in the other, Buccinopsis, very 

 like a whelk, the shell is finely striated. Putting them into form, 

 we have: 



Shell with curved canal 



Pillar folded at base Columbella. 

 Pillar toothed at base Nassa. 



Pillar smooth 



Coarsely ribbed Buccinum. 

 Finely striated Buccinopsis. 



There are five genera in which the canal is straight, and in one 

 of these, Murex, it is covered in so as to form a tube. Murex can 

 be identified at a glance by this tubular canal. Of the four with the 

 canal open, one, Triton, has the pillar with folds or tubercles, and 

 the shell is coarsely ribbed with very prominent varices. Both 

 species are large, being two or three inches long, and both are rare 

 as British specimens, and appear in our list as being found in the 

 Channel Islands. Among shells in general they are as well known 

 as any, being as old as Neptune, however old that may be, that sea- 

 god having used them before his trumpeter died. 



The three in which the pillar is smooth can be sorted out as 

 those in which the canal is long and those in which it is short. It 



