APPENDIX. 515 
are nothing more than the young conditions of Chiton asellus, 
which varies much in the dimensions of its longitudinal and 
transversal areas, as well as in the density and regularity of 
the linear punctated sculpture. Or we must conclude that 
these species are not in our collection, though we have been 
assured by good conchologists that our shells represent them. 
Since writing the above we have dissected specimens of 
both the so-called species, and found all the separate valves 
finely crenulate, not emarginate ; thus confirming the opinion 
that our shells are C. asellus. Therefore if Mr. Lowe’s 
C. aselloides—the C. albus of authors—is bi-emarginate on 
each side the valves, it cannot belong to the present species. 
It has however been suggested, that it may be a young, 
white, finely granulated C. cinereus; we should have con- 
curred in this view if it had not been opposed to so accurate 
an observer as Mr. Lowe. 
Our so-called C. cancellatus has the same finely crenulated 
margins as C. asellus, which is, we believe, the only British 
species thus sculptured. 
TROCHUS SERPULOIDES, p. 314; Tr. CurLerianus, p. 315 ; 
TR. NITENS, p. 316. 
Exmouth, 10th July, 1854. 
I have much satisfaction in stating, that the process under 
the right tentaculum in these very minute species, which is 
figured in a woodcut im the ‘Annals of Natural History,’ 
vol. vii. p. 45, N.S., and styled “ genitale,” has not that func- 
tion. Jam the more pleased with this discovery, as no such 
organ is to be found in that position in the large Trochi; and 
as these minute animals agree with their larger brethren in 
all other respects, [ was puzzled to account for this discre- 
pancy. The difficulty is removed by finding that the process 
I have alluded to is part of the right neck-lappet, which is 
bifid; both of its strands spring from the same membrane, as 
T have seen clearly in a brilhantly transparent’ Trochus nitens 
under high powers. The right neck-lappet is always longer 
than the left, which however is also bifid, but plain, and 
never ornamented, fringed or serrated, as is sometimes seen 
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