242 CHITONID#. 
found between the rectum and the posterior part of the 
ovarian sac. 
It has been said that the body is subannulate : in a hundred 
dissections we could not see much trace of such configuration, 
or breaks in it to correspond with the segmental arrangement 
of the valves; only slight marks, the effect of pressure, were 
observed. The connection of the Chitons with the Crustacea 
is, I think, so very slight and remote as to require no further 
notice. 
Having cursorily disposed of certain objections, we will 
proceed to state our own views, and in their course, allude to 
other objections and discrepancies. Though the Chitons are 
in closer alliance with the Bivalves, anatomically, by the 
arrangement of the circulatory apparatus, symmetry of the 
branchize, and by the absence of tentacula and eyes, than by 
the external hard parts; still in them, there are pomts of 
coherence which are not without their value: for mstance, in 
Pholas dactylus, which it almost immediately follows in our 
method, though the bivalve portion is not broken into regular 
segments, there are certain testaceous pieces, commonly, 
though perhaps incorrectly, called accessories, in number six, 
including the principal valves. We also find in the Chitons 
a subsymmetrical division into eight segments of what I con- 
sider essentially an integral patelloid cone, and as much 
accessorial as those of Pholas; indeed both in one and the 
other, these component parts are equally necessary and essen- 
tial. I admit that no great stress ought to be laid on the 
contrasted pomts; nevertheless, in conjunction with other 
decided anatomical analogies, they have their weight m the 
balance. 
Our view of the natural position of Chiton is after Dentalium, — 
with which it has marked affinities, and in immediate contact 
with the Patelloid group, in which we regard, in almost every 
respect, Fissurella as the point of comparison, as in it is seen 
the same form of the cone, though entire instead of broken, 
the same parity of the branchize, a similar posterior anal de- 
bouchure, and the attenuated mantle, gradually thickening, 
in both genera, to a tumid coriaceous margin, which in Fis- 
