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 7>. 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 Tr. maximus from the young Tr. niloticus. I 

 have at present before me two young maximus of this descrip- 

 tion, and two which are somew4iat older but retain the same 

 character J tbey 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 T. 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 wdiorls before the last, the sculpture both of the 

 upper and underside vanishes in Tr. niloticus, whdst in Tr. maxi- 

 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 Tr. niloticus concave above, convex 

 and smooth beneath — in Tr. 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, Columua, De Purpura, 



p. 21; Chemuitz, Conch.-Cab. v. pi. 167. fig. 1605, and pi. 168. 



fig. 1614 ; Encyclopedic Me'th. pi. 444. fig. 1 ; Kiener, Iconogr. pi. 10; 



Adams, Genera, pi. 46. fig. 7- 

 Trochus juvenilis, Listei", 680. 6 ; Chemnitz, v. pi. 167. figs. 1606, 1607. 



Tr. marmoratus. An. s. Vert. no. 

 Trochus pullus, Chemn. v. pi. 167. fig. 1610. Tr. spinosus, Gmel. Tr. 



marmoratus, var. (3, Philippi. 



II. Trochus maximus, Koch. Trochus pyramidalis maximus late radiatus 



ex rubra, Listei', Hist. Conch, no. 617. fig. 3 ; Philippi, Abbildungen, 

 i. pi. 4. fig. 3; Chemn. ed. nov. Trochus, pi. 19. fig. 4. Tr. marmo- 

 ratus, Kiener, Iconogr. pi. 11. Tr. niloticus, Reeve, Conch. Icon. 

 fig. 3. 

 Trochus pullus. Lister, 619. 5; Rumph. 21 b; Chemn. v. figs. 1608, 

 1609. Tr, niloticus, var. /3, Philippi. 



