256 PATELLID A. 
I will now shortly examine this condition, and at the same 
time include the comparison with the Tvrochi. 
Halhotis, i common with Fissurella, has a double symme- 
trical branchial plume, two auricles, and a ventricle embracing 
the rectum, which terminates between the roots of the bran- 
chie. The Zrochi have not an analogous pomt: in them, 
there is only one auricle and one branchial leaf, a heart not in 
contact with the intestine, and the rectum far removed from 
it, at the front of the right side. Again, the perforations are 
for the similar purpose of the fissure in the Fissurelle, for the 
dejections, and to admit the water to the respiratory vault. 
Nothing of this obtains in Trochus ; and further, the frmges 
and ornaments about the head, and the cordon of filaments in 
Halotis are in unison with Missurella and Emarginula. The 
Trochi, we admit, exhibit indices on these poits, and they 
are those which show the nearest approach to Halotis. In 
addition to these deviations, most malacologists would say, 
that Fissurella and Halotis are strict hermaphrodites, and the 
Trochi bisexual. I was of this opmion, but I believe that there 
are grave reasons to doubt this arrangement, and which lead 
me to consider the Trochi subject to one of the modifications 
of hermaphroditism. These views, and some other very cu- 
rious circumstances relative to them, will be communicated m 
our observations on the Trochide. And lastly, Fisswrella and 
Hahotis are without opercula, the Trochi never; the former 
are almost always fixtures, but the latter are locomotive. 
I have now gone through the principal anatomical and 
external aspects and habitudes of the contrasted objects, and, 
finding scarcely a point of community between them, I am 
bound to admit that Haliotis and the Fissurelle cannot be 
separated, and that the Trochi must rest where we have placed 
them in our method,—in the neighbourhood of their brethren 
that have circular opercula. 
If the genus Scissurella, now incerte sedis, does not belong 
to the Trochide, we should not be surprised to find that its 
position is near Haliotis. 
The Haliotis tuberculata is not strictly British ; it mhabits 
Guernsey and the other Channel islands. 
