. Natural history. Zoology. BIVALVESâVENUS SHELLS, COCI^'LES, ETC. 625 behind. The hinge plate is broader and there are no lateral teeth. As their name indicates, they are sand dwellers. A few occur on the British coasts, but the finer examples come from the Pacific and Indian Oceans. The DoNiCiD^s, or wedge shells, are very inequilateral, the front portion being much longer than the truncated hinder part. The exterior is usually smooth, the umbones are directed backwards, and the margins of the valves are usually very finely crenulated, whilst the pallial sinus is deep. There are two or three
. Natural history. Zoology. BIVALVESâVENUS SHELLS, COCI^'LES, ETC. 625 behind. The hinge plate is broader and there are no lateral teeth. As their name indicates, they are sand dwellers. A few occur on the British coasts, but the finer examples come from the Pacific and Indian Oceans. The DoNiCiD^s, or wedge shells, are very inequilateral, the front portion being much longer than the truncated hinder part. The exterior is usually smooth, the umbones are directed backwards, and the margins of the valves are usually very finely crenulated, whilst the pallial sinus is deep. There are two or three cardinals and two laterals, one anterior and one posterior, in each valve. The Tancrediidjb have very similar shells to the Donacidre. The MactriDjB are a large and widely-distributed family dwelling in sand. The shell is equivalve and somewhat triangular; commonly smooth and white, with a trace of periostraoum. The hinge is usually marked by the conspicu- ous internal resilium lodged in a deep pit ; but in some forms the whole ligament is external. The hinge-plate is well developed ;â the teeth vary somewhat, typically there is a A-shaped cardinal tooth in each valve in front of the resilifer, and single anterior and posterior lateral teeth in the right valve fitting into double ones in the right one. , The Cardiliid^, are very similar in their shell to the preceding, and are probably closely allied to them, but their anatomy is still unknown. ' The Mesodbsmatid^e resemble the Mactridaj in their anatomy, but the siphons are not united, the shell usually is more like that of Donax with umbonea directed backwards. Sub-order 3âVeneracea. These have usually short siphons, and there- fore a moderate pallial sinus. The shells of the principal family, Venerid^, are remarkable for the elegance of their forms and colours. Their texture is very hard and procellaneous, the exterior is frequently smooth and highly polished, sometimes ornamented with V-shaped lines of
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Keywords: ., bookauthorly, bookcentury1800, bookdecade1890, booksubjectzoology
