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VIII. On the Anatomy of the Lamellibranchiate Conchifera. By Ropert Garner, 
Esq., F.L.S. Communicated by Ricuarp Owen, Esq., F.R.S. 
Communicated December 8, 1835. 
THE molluscous animals, the anatomy of which I propose to describe, whilst they are 
distinguished from the Tunicata' by their calcareous parts, differ from the Brachiopo- 
dous Conchifera by being furnished with two lateral lobes to the mantle, secreting a 
right and a left valve; by having commonly an elastic intervalvular cartilage, and a 
more simple muscular system to open and close the shells; by having also four fixed, 
membranous, pectinated organs at the mouth, and four others for respiration, &c. 
The Anomia I consider to be an intermediate genus between the Lamellibranchiata 
and the Brachiopoda ; some parts of its structure being more in unison with that of the 
former, and some with that of the latter. The position of the animal in the shell is 
neither vertical as in the one, nor horizontal as in the other, but oblique with respect 
to the disposition of its organs. It agrees with Orbicula in having a divided muscular 
system, a rudiment of a pedal disc, a short intestinal canal, ovaria ramified in the 
mantle, the labial and branchial appendages conjoined, &c.; whilst in other respects it 
resembles the Monomyarious Lamellibranchiata. 
I would suggest that the fossils called Spherulites are allied to the Anomia, and 
would intimate how desirable it would be to examine the anatomy of Thecidea, Crania, 
Placuna, and the different species of Anomia, Terebratula, &c. 
Some degree of obliquity, and a difference of size in the two valves, is present in 
many genera of Lamarck’s first division Monomyaria ; whilst, if any inequality exist in 
those of his second division, Dimyaria, it does not arise from a tendency, as in the former 
case, to that relative position of the soft parts to the shell, which characterizes the - 
Brachiopoda, but results from the nature of the hinge. 
It is unnecessary here to enter upon the affinities of the order, or to describe the growth 
of shell. In the distant layers of shell in the valves of some Lamellibranchiata I think I 
see a resemblance to the elongated cellular valves of certain fossil genera and to multilo- 
cular shells. The figure and size of the foot influence most materially the form of the 
anterior part of the shell ; whilst that of the posterior is dependent upon the modifications 
of the siphons. In order to explain the remoteness of the beaks of the valves in some 
' I find in some British Twnicata calcareous pieces, under the form of two conical, reticulated tubes, 
situated in, and projected externally from each orifice of the tunic. These, overlooked by Savigny, were 
found by Eysenhardt. 
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