IDENTIFICATION. 77 



sign of a groove or canal in its periphery ? If so, we can at once 

 take a long stride onwards, and ask if it is transparent ; which it is 

 not. And so it has both a groove and a canal, as it happens, and it 

 is decidedly opaque, being, in fact, rather thick and heavy. Is it 

 convolute ; that is, does its outer lip turn in so as to make a long 

 narrow mouth as in the cowry ? No. Is it fusiform, with a long 

 and narrow mouth ? No ; neither has it a curved canal, but the 

 canal is covered over and is like a tunnel through the shell. That is 

 enough ; the genus is Murex, and if the canal had been continued 

 down a long tube, the genus would still be Murex. 



Let us take another genus, often confused with it, and answering 

 all our questions in the same way up to here. The canal is not 

 covered but open, and is decidedly short. Hence the genus is 

 Purpum, and as the ridges are alternately large and small the 

 species is lapillus, although sometimes the ridges of that species are 

 all of the same size ; and it has the teeth in the throat, which most, 

 but not all, of its representatives have, for lapillus has so many 

 variations that only three of its varieties have been thought worth 

 mentioning. 



Here is another, in which the margin of the mouth is without a 

 groove or canal. The shell is neither tubular, nor globular, nor ear- 

 shaped, nor cap-shaped, nor is the mouth toothed. It is not coiled 

 flat, and that clears us of four genera ; but it is a raised spiral. The 

 pillar does not project beyond its mouth, its apex is not divided into 

 two. nor is it broken off short, and its outer lip is not slit, so we can 

 pass half-a-dozen more genera. Its height is not less than its 

 breadth, that clears away seven more genera. But its height is less 

 than double its breadth, and that leaves us among four genera, from 

 which it can be separated by its having a fold in its pillar. The 

 genus is Limnaa, and a reference to the index of geneia will show 

 that the species is stagnalis. 



Yet one more. The margin of the mouth without a groove or 

 canal, no teeth, the shell not coiled flat, the shell a raised spiral, the 

 height less than double the breadth, peristome complete, the pillar 

 without a groove, dextral, not amber-coloured, not richly variegated 

 and polished, not with the inner lip thick and the outer lip sharp, 

 the shell not thin but moderately thick, the mouth nearly circular. 

 At last I The genus is Cyclostoma, of which there is but one species, 

 elegans, found mostly on the chalk and rarely in other limestone 

 districts, and it is worth knowing as being one of the two British 

 land shells that have an operculum. 



