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 inclined 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 (pl. 3. fig. 21), Gualtieri 
(pl. 59. fig. c), and Argenville (pl. 8. fig.c) seem to represent 
rather 7. 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 
(2. 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 i is added, 
we cannot tell with certainty whether the true 77. 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 Linné; 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 Zr. 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 Tir. niloticus and Tr. maximus. Nevertheless there are 
some traces of another habitat for Zr. 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 617.38. 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 
