Trochus niloticus and Trochus maximus. 99 
niloticus are almost as broad, regular, and few as those of 77. 
maximus: such a specimen of Tr. niloticus is figured by Chem- 
nitz. The measurements of the largest and of the smallest 
specimens, which may be supposed to be full-grown, among 
those exhibited in the Berlin Museum are as follows, the height 
being measured from the top to the undermost part of the pillar 
side of the aperture :— 
Tr. maximus: height 130, breadth 130; height 91, breadth 91 millims. 
RR gs SEA se: ADA. gy Oli un 87 
The last measurements are taken from an extraordinarily dwarf 
specimen, the thickened pillar-lip and convex basis of which 
prove it to be full-grown. 
In almost every full-grown specimen of TJ’. niloticus the 
uppermost whorls are much worn and often wholly destroyed ; 
this circumstance has probably hitherto formed the chief diffi- 
culty in recognizing the very young specimens as belonging to 
the same species. Iam compelled by it also to number the 
_ whorls in a retrograde manner, from the last upwards. The two 
whorls before the last in Tr. niloticus are, as above stated, 
even, smooth, and marbled; they agree in these respects, as 
well as in size, exactly with the last two whorls of 7. marmoratus 
as figured by Chemnitz (figs. 1606, 1607) ; and on placing several 
specimens in the Berlin Museum agreeing with those figures 
side by side with the full-grown niloticus, I feel quite convinced 
that they are nothing but the same species in a younger state, 
wanting the last whorl. The base of one of these specimens is 
as smooth as that of the full-grown niloticus; the base of an- 
other exhibits distinct traces of spiral grooves; in all, however, 
it is neither convex nor concave, but as even as the spiral 
growth allows it to be. The second whorl before the last in 
Tr. marmoratus exhibits a sculpture of large plaits or tubercles 
near the lower edge, and two or three rows of small grains above 
them, sometimes uniting themselves into oblique plaits, vanish- 
ing gradually towards the upper whorls; therefore the third 
before the last in the full-grown niloticus must have the same 
sculpture; but this is just withm reach of the apical destruc- 
tion, so as to show only few and less distinct traces of the sculp- 
ture in question. Moreover there are in the Berlin Museum 
smaller specimens agreeing perfectly with Gmelin’s Trochus spi- 
nosus, Chemnitz, fig. 1611, in size, shape, and sculpture, which, 
on comparison with those named marmoratus, prove evidently to 
be the young of the same—that is, the very young niloticus, 
requiring still three or four whorls for its full age, and therefore 
sculptured on all the whorls which have been as yet formed. 
In these specimens, also, the base is even and slightly grooved 
in a spiral direction. 
7* 
