DENTALIUM. 229 
I have not detected auricles on each side of the heart, nor 
near it, as might be expected from the symmetry of the 
branchiz ; there are certainly minute points on each side of 
that organ, but I object to call them auricles, and rather 
think they denote the valvular appendages of the heart, to pre- 
vent regurgitation into the branchial vems. The blood of the 
posterior part of the body is brought to the branchial artery 
which runs at the inner base of the branchie, by two longi- 
tudinal veins, which pass between the branchize on their 
convex surface, receiving tributaries ; I could not trace those of 
the anterior part. The arterial blood is then distributed into 
the ramifications of the branchize, and after aération is passed 
by each principal vein, which coasts the edges of those organs 
at their dichotomous points, to the heart, which throws out a 
posterior and anterior short trunk, both of which bifurcate 
ito two smaller arteries, which supply veims infusing a re- 
newed vitality into all parts of the body, from whence the 
blood is again returned to the arterial centre. Under the 
microscope the blood of the tributary and superficial veins 
appears to be in some individuals of a pale pmk colour, and 
in others of a purplish pale red cast. 
The branchize are two symmetrical, sublateral, and some- 
what post-centrally situated, dark greenish-brown, elongated, 
suboval organs, having their bases fixed on and hanging from 
the concave surface of the animal, with their points vertically 
parallel to the bases; the two branchiz are united at their 
inner surfaces by a bridle of branchial strands arranged sym- 
metrically. 
The heart in the testaceous Gasteropoda, spiral and other- 
wise, is always placed at the posterior end of the branchial 
cavity, or, in other words, is fixed at that extremity of the 
branchi furthest from the entry of the aérating fluid*. This 
* M. Milne-Edwards has placed a few genera, as Bulla, Pleurobranchus, 
and Aplysia, in his division Opisthobranchiata, as having the heart anterior 
to the branchiz. Without closely considering the merits of his arrange- 
ment, which perhaps is fine-drawn and not constant, we may say, in respect 
of the case between M. Deshayes and myself, that it does not bear upon it, 
as, in whatever way the question is looked at, Dentalium is a strict proso- 
branchiate animal, with the branchie anterior to the heart. 
