irochus niloticus and Trochus maximus. 101 



In Lister's figure 3 the base seems rather convex than con- 

 cave; but, as the other characters agree with Tr. maximus, I 

 feel inchned to think this may be a fault of the engraver; or 

 may it be a form intermediate between the two ? 



The figures in the works of Rumph (pi. 3. fig. 31), Gualtieri 

 (pi. 59. fig. c), and Argenville (pi. 8. fig. c) seem to represent 

 rather Tr. maximus than Tr. niloticus. 



Trochus niloticus is an inhabitant of the Indian seas. I found 

 it myself alive on the coral beach of the little island Pulo-tikus, 

 near Bencoolen, Sumatra. Quoy and Gaimard (Voyage of the 

 Astrolabe) describe the living animal, found by themselves at 

 New Ireland. Philippi mentions as a locality for Tr. marmoratus 

 {i. e. the young niloticus) the Sooloo Islands, south of the 

 Philippines. Other localities, which may be got out of various 

 published lists of sea-shells found at Ceylon, Madagascar, &c., 

 may be here omitted, as, where no description or figure is added, 

 we. cannot tell with certainty whether the true Tr. niloticus or 

 Tr. maximus is meant. The name Trochus niloticus itself is 

 consequently incorrect : it originated with old Aldrovandi (who 

 gave it, equally incorrectly, to a large species of Conus), and was 

 transferred to our Trochus by Linne ; but as it is now generally 

 adopted and so evidently untrue that no misunderstanding is to 

 be feared from it, I would not propose to change it for a new one. 



The habitat of Tr. maximus has not been stated by Koch and 

 Philippi. I procured a young specimen at Singapore, and 

 think therefore that the Indian Ocean is the common home of 

 both Tr. niloticus and Tr. maximus. Nevertheless there are 

 some traces of another habitat for Tr. maximus : in the Berlin 

 Museum there is a very young specimen of the latter, stated by 

 a label to have formed part of a collection made in Guinea by 

 Mr. Halleur (the other shells of the same collection are true 

 West-African species) ; and Chemnitz informs us that, in his 

 copy of Lister's work, a manuscript note, " ex insula Principis," 

 was added to the said figure 617. 3. If this is the island situated 

 in the Gulf of Guinea, it would be in favour of the West- African 

 habitat ; or are we perhaps allowed to presume that the Prince 

 of Wales Island, i. e. Pulo Pinang, on the coast of Malacca, 

 was meant ? It is very desirable that more reliable statements 

 concerning the habitat of this form, Trochus maximus, should 

 come to our knowledge. 



I never saw a full-grown specimen which left any doubt 

 whether it belonged to the one or the other species : the diffi- 

 culty of distinguishing them increases the younger the indivi- 

 duals are which come under observation, and the more so as 

 even the different stages of age in which the characteristic 

 changes of feature make their appearance are subject to a certain 



