1. The Veneridæ. The hard, solid shells of this family are for elegance of form and beauty of colour amongst the most attractive a collector can posses. Their shells are more or less oval and have three teeth in each valve ([Fig. 20]).
2. The Mactridæ are somewhat triangular in shape, and may be at once recognised by the pit for the hinge-ligament, which also assumes that form, as seen in the accompanying figure of Lutraria elliptica ([Fig. 21]).
3. The Tellinidæ comprise some of the most delicately tinted, both externally and internally, of all shells. In some, coloured bands radiate from the umbones, and well bear out the fanciful name of "Sunset shells" bestowed upon them. Their valves are generally much compressed.
4. The Solenidæ, or "Razor-shells," rank next, and are readily recognised by the extreme length of the valves in proportion to their width, and also by their gaping at both ends.
5. The Myacidæ or "Gapers," have the siphonal ends wide apart (in the genus Mya both ends gape), and are further characterized by the triangular process for the cartilage, which projects into the interior of the shell. One valve (the left) is generally smaller than the other.
6. The Anatinidæ have thin, often inequivalve pearly shells. The genus Pandora is the form most frequently met with in collections.
7. The Gastrochænidæ embraces two genera (Gastrochæna and Saxicava) of boring mollusca, which perforate shells and rocks, and also, the remarkable tube-like "Watering-pot-shell" (Aspergillum) which is hardly recognisable as a bivalve at all.
8. The Pholadidæ concludes the list of bivalves, and comprises the common rock-boring Pholas ([Fig. 22]) of our coasts and the wood-boring shipworm "Teredo" ([Fig. 23]).