212 
TROCHUS abbreviatus. 
TAB. CXCIIi.--- Fig. 5. 
Spec. Cuar. Conical, shortened, transversely stri- 
ated; strize obscurely decussated by oblique 
lines of growth ; inferior margin of each whorl 
very prominent, obtuse, with an obscure band 
above it. 
aan) eae 
Brraptn greater than the height ; the prominent mar- 
gins of the whorls are marked by semicircular lines; but 
they are not regular, being only lines of growth. The base 
is sharply striated. 
This Trochus, and the two species above described, 
were sent me by George Weare Braikenridge, esq. who 
collected them at Dundry. I understand that they are not 
such perfect specimens as might perhaps be obtained at 
some future period, but I am anxious to make them public 
on acount of their near resemblance to some Trochi found 
in a similar stratum in Normandy, of which I have given 
one or two of the products in illustration of Ammonites 
Braikenridgii. The 'Trochi I allude to have largely cre- 
nulated margins, which at once distinguish them; but one 
ofthem is characterized by sharp numerous elevated striz, 
which cross the whorls obliquely on their upper parts, and 
in semicircles over the band and prominent inferior mar- 
gin; there are vestiges of such striz in the species before 
us, but the French shell differs also in having a greater 
number of transverse strie, and being of a longer form, 
itis most like Trochus elongatus. They all have solid co- 
lumelle. It appears very remarkable to me, that strata 
agreeing together in their composition so closely should 
produce several shells resembling each other, but, as far 
as I have hitherto learnt, none are precisely the same. I 
wish to instigate further research. It is a circumstance 
corresponding with provincial differences among man- 
kind; whether such differences among shells should be 
considered as specific, may remain a question. 
