BIVALVES. 



4i3 



and large labial palpi and foot. The shells are nearly always compressed, subequi- 

 valve, joined by an external ligament, and furnished with hinge-teeth. The scars 

 of the adductors are far apart, and the pallial impression is generally very deeply 

 sinuated. None of the bivalves are more beautifully coloured than the tellens, 

 the prevailing tints being purple-red, crimson, and various shades of yellow. 

 The surface-sculpture of the valves is often beautiful and delicate. Tellens live 

 in sand or mud at slight depths in every sea, and the species may be counted in 

 hundreds. Nine species of Tellina are British. The Scrobiculariidce form a 

 smaller and less showy family than the preceding, the shells being united by an 

 internal ligament, and sometimes by an external one also. The soft-parts are 

 like those of the Tellinidm. Some species of the genus Abra have been dredged 

 at enormous depths, both in the Atlantic and Pacific, but the majority of the 

 family have been obtained in comparatively shallow water. The British Scrobi- 

 cularia piperata buries itself in the mud of estuaries, and can extend its siphons 

 five or six times the length of its shell. Although in some respects the wedge- 

 shells (Donacidce) agree with the Tellinidce, they differ as regards the gills. In 

 Donax the shells are of a triangular or wedge-shape, and have the inner margin 

 of the valves crenulated. They are united by an external ligament, and furnished 

 with cardinal and sometimes lateral teeth. The wedge-shells live buried in the 

 sand in shallow water in warm regions all over the world, and three species occur 

 on the British coasts. The genus Iphigenia, which has no lateral teeth, inhabits 

 estuaries on the coast of Africa, Brazil, the West Indies, and Central America. 

 In the mactras (Mactridce) the shells are often more or less triangular, and 

 have an internal ligament, the siphons being united the entire length, and 

 fringed at the ends. About one hundred and fifty species of Mactra are 

 known. They occur on sandy shores in most parts of the world at shallow 

 depths, six being British. This family comprises a large number of genera and 

 subgenera, mainly distinguished by modifications of the hinges ; Mulinia, 

 Spisula, Standella, Rangia, Rceta, and Eastonia being the more important. The 

 remaining familes, Mesodesmatidce and Cardiliidce, are not of special importance, 

 and may be passed without further reference. 



Suborder Veneracea. 



In the Veneridw, which form the first family of this group, the animal 

 has rather short, more or less united siphons, with fringed openings. The 

 mantle is open in front for the passage of a tongue-like foot, which is sometimes 

 furnished with a byssus. The shells are solid, equivalve, and often beautifully 

 coloured and sculptured, with the hinge-teeth large and divergent, and the 

 ligament external. In the typical genus Venus the shells are more or less 

 circular, globose, and often have the surface cancellated, and the inner edge of the 

 valves crenulated. There are several British forms of Veneridce, but none are 

 eaten to any great extent. On the contrary, the large Venus mercanaria — the 

 clam of the Atlantic States of North America— is sold in large quantities in 

 the fish-markets of New York and Philadelphia. In Dosinia the shells are 

 more compressed, circular, and marked within with a deep, narrow, pallial 



