INTRODUCTION, 9 
carine or kee]s running across the shell, and in shells very closely 
allied to them we find that the characters so prominent in the noduled 
shells have completely changed and become smooth. ‘This is a 
change from one of the roughest examples of external character to 
the smooth unsculptured shell. Specimens that are intermediate in 
sculpture and possessing both forms, that is, the pustules or 
nodules on the ribs, and those with nodules at the junction of the 
intersecting lines, may be seen in the N. tritoniformis, Kien. The 
occupation of the squares by rounded papille occurs in the shells 
of N. gemmulata, Lam., from Ceylon, but the Philippine variety, 
as figured in Reeve at pl. 5, f. 29, is a ribbed shell, with intersecting 
cross-grooves, and every intermediate variety connecting the two are 
in a tray lying before me. The best examples of the third kind of 
pustules, viz., those occurring at each corner of the squares formed 
by the junction of the transverse and longitudinal lines, may be 
seen in the N. reticosa, A. Ad., N. Roissyi, Desh., N. cremata, 
Hinds, &c. N. candens of Hinds presents another modification of 
this last ornamentation ; instead of the squares being distinct we 
have one, two, or even three transverse lines occurring between 
the principal ones, making the whole surface very irregular. A 
similar instance of intermediate transverse striz occurs in the varieties 
of N. sordida, A. Ad., from Australia, and I think it is very pro- 
bable that the large variety of N. Gruneri, D’k’r., viz., the N. echinata, 
A. Ad., isa tubercular variety of N. sordida. None of these shells 
have permanent characters, nor can they be of any value specifically, 
inasmuch as there is no depending upon them. Ina tray before me 
are four shells of N. cremata, Reeve, all collected together, and to 
all appearance in form, colour, and marking they are similar; but 
the pocket glass shows at once that there are no two of them alike ; 
one has the squares similar to the figure in Reeve, the next forms 
parallel ribs in which the parallelograms are very narrow and 
elongated, a third shows a tendency to become pustular. Another 
tray has three shells in it, and these, like the last, were all 
obtained at one station and, if I am rightly informed, they all came 
up at one haul of the dredge ; the nearest figured shell to which 
they may be referred is the N. marginulata, Lam., Kein., pl. 29, 
