TRUNCATELLA. 385 
ranged in transverse order. The only difference observable in 
the two species is, that in this, the leaf appears of a shorter or 
more oval contour, more compact, and with a less deep con- 
striction ; the neck and rostrum have no additions beyond the 
groove and aunulations. Foot thick, having a more elongated 
oval shape than in its congener, and, as in it, rounded in front 
and behind on the march; it simulates the same transverse 
crease or line on the sole, and has a lke character of pro- 
gression. There is a simple, almost terminal, but decided 
operculigerous lobe that bears a light corneous suboval oper- 
culum, which in all points, except beimg of lighter colour and 
broader oval, is identical with that organ in the preceding 
species, to which I refer ; indeed, so great is the similarity of 
the two animals, that I might, by a reference, have condensed 
the greater part of this account; but as these notes are 
decidedly comparative of two particular creatures, I have 
given them in extenso. The animal is free, but deliberate 
on the march, and carries its shell very upright, at nearly an 
angle of 75°-80° from the horizon. 
It will be seen that this account is essentially the same as 
the one in the ‘ British Mollusca,’ except that the learned 
authors have proposed to deposit it in Assiminia. I think its 
generic position is with Zruncatella. A comparison of the 
two species will show that they are not only identical in the 
principal characters, but that almost all the minutiz are con- 
gruous. Indeed I may say, that these gentlemen differ from 
me little more than in the name, ‘ Assiminia, which I would 
gladly accept for Truncatella for the reasons below, if such 
a change in nomenclature were not forbidden by strict con- 
ventional laws. As far as I can learn, not having seen the 
animal of 4A. Grayana, the genus Assiminia scarcely varies, if 
at all, from Truncatella; at least the generic characters given 
in the ‘ British Mollusca’ are absolutely those of that genus, 
except some difference in the position of the eyes, which I 
should not be surprised to find greater in terms than in reality. 
The generic title of Truncatella is objectionable, as being 
in this case too distinctive, and therefore only strictly appli- 
cable to Truncatella Montagui, whilst two, if not three, of our 
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