On the different Ages of Troclms uiloticus and T. maximus. 97 



this hypothesis supposes a very great antiquity for these species. 

 But this antiquity has its parallel in the Helix labyi-inthica of 

 North America, which is found in the Eocene deposits of the 

 Isle of Wight ; and there are many circumstances which tend 

 to show a high antiquity for the species of terrestrial Mollusca. 

 Port-of-Spain, Trinidad, June 4, 1867. 



XIII. — Conchological Gleanings. 

 By Dr. E. von Martens. 



I^Contiuued from vol. xvii. p. 213.] 



V. On the different ages of Trochus niloticus, L., and 

 Tr. maximus, Koch. 



Trochus niloticus is one of the commonest shells in our col- 

 lections ; nevertheless it seems not to have been fully understood 

 as regards its several stages of growth and its differences from 

 its nearest ally Tr. maximus, Koch, which, indeed, is figured in 

 Reeve^s 'Conchologia Iconica^ instead of the true niloticus. 



Chemnitz^s ' Conchylien-Cabinet,^ the most complete work on 

 conchology of the last century, contains, in its fifth volume, 

 published in 1781, four shells, said to be of different species, 

 which are to be referred as follows : — 



Figs. 1605 and 1614, the true Tr. niloticus of Linue, full- 

 grown. 



Figs. 1606 and 1607, registered by Gmelin as a variety of the 

 former, by Lamarck and Philippi (in Kiister's new edition of 

 Chemnitz) as a distinct species, Tr. marmoratus, Lam.; by Dill- 

 wyn, Deshayes, and Anton, on the contrary, as the younger 

 age of Tr. niloticus. This latter opinion seems to me to be 

 correct. 



Figs. 1608 and 1609, cited only by Philippi {loc. cit.) as a 

 variety of niloticus, " which may be perhaps a distinct species,'^ 

 I think is a young state of Tr. maximus. 



Fig. 1611, called by Gmelin Tr. spinosus, regarded byPfeiffer, 

 in his index to Chemnitz's figures, with some doubt, as a young 

 marmoratus, and by Philippi as wormorc^MS, var. /3. I suppose 

 it to be a Tr. niloticus still younger than fig. 1606. 



The full-grown Tr. maximus, Koch, was not inti'oduced as a 

 distinct species before the year 1844, when it was figured in 

 Philippics 'Abbildungen und Beschreibungen neuer Conchy- 

 lien ',' it a])pears again in the same author's treatise on the 

 genus Trochus, which forms a part of the above-mentioned nev^ 

 edition of Chemnitz, in Kiener's ' Iconographie,' with the name 

 Tr. marmoratus, and in lleeve's ' Conchologia Iconica' as an 



Ann. 6f Mag. N. Hist. Ser. 3. Vol. xx. 7 



