. Bulletin of the British Museum (Natural History). Zoology . SHELL STRUCTURE OF THE BIVALVIA 73 We have examined Solemya australis by scanning electron microscopy, and find that within the conchiolin prism walls the aragonite is deposited as irregular plates and grains, apparently without any regular orientation in some chambers, although in others the grains seem to be deposited as a more regular surface (Plate 12, figs. 1-4). The calcareous parts of the shell of Solemya have a high organic content, and the amino acid composition and histochemistry have recently been investigate
. Bulletin of the British Museum (Natural History). Zoology . SHELL STRUCTURE OF THE BIVALVIA 73 We have examined Solemya australis by scanning electron microscopy, and find that within the conchiolin prism walls the aragonite is deposited as irregular plates and grains, apparently without any regular orientation in some chambers, although in others the grains seem to be deposited as a more regular surface (Plate 12, figs. 1-4). The calcareous parts of the shell of Solemya have a high organic content, and the amino acid composition and histochemistry have recently been investigated by Beedham and Owen (1965). According to these authors, the non-calcareous organic matrix of the shell is made up of two types of conchiolin which they term " A ' and ' B \ The outer layer contains their type ' A ' conchiolin which makes up 4*5% by weight of this part of the shell, and forms the prism walls. The organic matrix of the inner shell layer is mostly type ' B ' conchiolin. The two conchiolins have different amino acid compositions and the conchiolin in the outer layer is appreciably tanned, whereas the conchiolin of the inner layer is only lightly tanned. Sub Class PTERIOMORPHIA Order ARCOIDA ARGACEA (Plate 15, fig. 1 ; PI. 18, fig. 1 ; PI. 19, figs. 3, 4, 5 ; PI. 21, fig. 4 ; PI. 22, figs. 1, 2 ; PI. 29 ; text-figs. 40-42) Nineteen species of the group have been examined mineralogically and twelve optically (Table 4). The shell is aragonitic throughout. Two main shell layers are present, an outer crossed-lamellar layer which forms the hinge and teeth, and an inner complex crossed-lamellar layer which is bounded by the trace of the pallial myostracum. In the outer crossed-lamellar layer, the first order lamels are arranged concentrically over the whole shell, except. prismatic pallial myostracum Fig. 40. Arcacea : General view of the interior Anadara scapha auct. showing the distribution of the shell-layers Please note that these images are extracte
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