10 INTRODUCTION, 
f. 117; the first has square spaces, the second is ribbed and transversely 
grooved, and in the third the ribs are drawn up into sharp edges. 
Another tray containing four specimens exactly intermediate 
between the N. cremata, Reeve, and the N. marginulata, Lam., pre- 
sent still greater differences, inter se: the first has squares on the 
upper part of the body-whorl, each being divided by a grooved 
line ; then the sculpture changes and the centre of the whorl has 
rounded—almost pustular ribs, and at about one third of the 
length of the whorl from the base the knotted squares occur, so that 
the three principal forms of sculpture are here present on the one 
shell; in another specimen the ribs are distant and simply intersected 
by cross-grooves ; the callous of the columella also differs in each of 
the specimens ; in the first it is thick and spreading, in the next it 
is less so, in the third it is still less, and in the fourth it is 
almost confined to the edge of the columella. The shells of N. 
sequijorensis, A. Ad., are for the most part of a character intermediate 
between the shells with smooth ribs and the cancellated varieties ; 
they are finely or coarsely ribbed, some of them are smooth in the 
interstices between the ribs, others have a few sulci, and again we 
have the sulci close and numerous ; in some specimens the ribs are 
smooth, in others they are sparingly cross-grooved, and lastly they 
are closely cancellated. Neither colour nor texture appear to be of 
any use in attempting to decipher the shells in the group to which 
N. sequijorensis, A. Ad., belongs ; some of its varieties are white 
with pale rufous bands, and intermediate forms connect these with 
shells that are as nearly black as it is possible for shells to become. 
The texture is sometimes almost hyaline and the shells are thin, and 
these are connected by intermediate forms with others that are 
thick and heavy. The sutural canal in one specimen is closed or 
only represented by a fine line, but the specimens gradually change 
until it becomes rather widely expanded; the prickly serratures on 
the lip vary from the smallest and most simple rudimentary forms 
to the fullest state of development. 
The greater part of the shells figured and described as new 
species have for their recommendation to our notice a single speci- 
men, and that often in bad condition. Men are so anxious to have 
