100 Dr. E. von Martens on the different Ages of 
This sculpture is the same as that of the upper whorls in 
Trochus maximus ; the striking differences between the two spe- 
cies enumerated above in Nos. 3-5 are situated in the last 
whorl, The markings on the upper whorls of marmoratus are 
nearly the same as in maximus ; therefore the only differences by 
which we are able to distinguish the very young 77. niloticus 
from a Tr. maximus of the same age are the somewhat broader 
shape of the whole shell and the somewhat larger apical angle. 
But whenever the specimens have reached about 40 millimetres 
in diameter, or about the fifth or sixth whorl (the third before 
the last in full age), the persistence of the sculpture and the 
deepening spiral grooves of the base will undoubtedly distin- 
guish the young 77. maximus from the young 77. niloticus. I 
have at present before me two young maximus of this deserip- 
tion, and two which are somewhat older but retain the same 
character; they agree very satisfactorily with Chemnitz’s figures 
1608 and 1609: in these specimens also the base is neither 
convex nor concave, but even; the markings show the charac- 
teristic features of 7. maximus. 
Thus three periods may be distinguished in the course of life 
of the two species: in the first, which extends until the fifth or 
sixth whorl, both are very like each other; in the second, com- 
prising the two whorls before the last, the sculpture both of the 
upper and underside vanishes in 77. niloticus, whilst in Tr.mazi- 
mus the upper one becomes only more feeble, and the under one 
even increases in strength; in the third period, finally, the 
differences between the two species prove to be quite contrary, 
the last whorl becoming in 77. niloticus concave above, convex 
and smooth beneath—in Jr. maximus nearly straight above, 
concave and deeply furrowed beneath. 
The synonymy of the two species may be resumed as fol- 
lows :— 
I. Trochus niloticus, L. Turbo exoticus umbilicatus, Columna, De Purpura, 
p- 21; Chemnitz, Conch.-Cab. v. pl. 167. fig. 1605, and pl. 168. 
fig. 1614; Encyclopédie Meéth. pl. 444. fig. 1 ; Kiener, Tconogr. pl. 10; 
Adams, Genera, pl. 46. fig. 7. 
Trochus juvenilis, Lister, 680. 6; Chemnitz, v. pl. 167. figs. 1606, 1607. 
Tr. marmoratus, An. s. Vert. no. 
Trochus pullus, Chemn. v. pl. 167. fig. 1610. Tr. spinosus, Gmel. Tr. 
marmoratus, var. 8, Philippi. 
Il. Trochus maximus, Koch. Trochus pyramidalis maximus late radiatus 
ex rubro, Lister, Hist. Conch. no. 617. fig. 3; Philippi, Abbildungen, 
i. pl. 4. fig. 3; Chemn. ed. nov. Trochus, pl. 19. fig.4. Tr. marmo- 
ratus, Kiener, Iconogr. pl. 11. Tr. niloticus, Reeve, Conch. Icon. 
fig. 3. 
itroekes pullus, Lister, 619.5; Rumph. 218; Chemn. v, figs. 1608, 
1609. Tr. niloticus, var. B, Philippi. 
