34 SHELL GALLERY. 



the Asiphonida. The former (Cases 17 e to 21b) include such 

 species as have the mantle prolonged posteriorly into tubular 

 siphons for the admission of water to the gills; and the edges of 

 their mantle are more or less united. 



The Asiphonida (Cases 21 c to 25 a) are destitute of siphons, 

 and have the mantle-margins free. These two main divisions 

 have been subdivided into minor sections characterized by differ- 

 ences in the foot and gills, by the presence or absence of a sinus 

 in the pallial line, the number and position of the hinge -teeth, and 

 the character of the ligament. 



SlPHONIDA. 



Cases The first family, Veneridce, have long respiratory siphons and 



17E-18C.J a smua t ec l pallial line. Many of this tribe are very beautiful in 

 form and colouring, and most of them have very hard strong shells. 

 The valves are united above by an external ligament, and the hinge- 

 plate is toothed. Nearly all of them live buried an inch or two 

 beneath the sand or mud, but a few are found burrowing in rocks. 

 Probably the majority of the species of this family might be used 

 as food. Venus verrucosa, of our own southern shores, is frequently 

 eaten both in this country and abroad ; and Venus mercenaria is 

 commonly sold in the markets of Philadelphia and New York. 

 Cytherea lusoria also forms a favourite article of diet among the 

 poorer classes in Japan, and several kinds are eaten by the natives 

 of New Zealand and other countries. 



[Case Of the CorbiculidcB, the genera Cyrena, Batissa, and Velorita 



are found in brackish water at the mouths of rivers or in Man- 

 grove swamps, and the smaller forms, as Corbicula, Spharium, and 

 Pisidium, live in fresh water. 



["Cases The Tellinas have usually thinner shells, and their two siphons 



E_ B * are longer and more completely separated from each other than in 



the Venerids. The pallial line is widely and deeply sinuated, and 



the ligament generally external, except in the genus Semele, where 



it is placed within the hinge-margin. They live in great numbers 



beneath the sand in shallow water, and are occasionally used as 



food. 



[Case 19, The Mactridce have an internal ligament to the hinge, the siphons 

 r>-r>.'J 



