VI INTRODUCTION TO 



times accessory plates. The shell of Xylophaga, 7, is like that of Teredo > 

 but the animal has neither pallets nor tube. 



Gastrochcena, 14, has a gaping shell, and encloses itself in a bottle- 

 shaped covering of cemented stones and sand. Saxicava, 15, 16, Ve- 

 nerupis, 18, and Petricola, 17, burrow in sand, or live in holes of rocks. 



Myada, or '/Gapers," My a, 19, 20, and Panopcea, 21, 21*, burrow 

 downwards in sand and mud, their siphons protected by a coriaceous 

 covering. Their shells are not closed all round, and those of Mya have 

 a spoon-shaped process in the hinge of one valve. 



Corbulidce, 22-28, have short siphons with fringed edges, and the 

 foot protrudes through a hole in the otherwise closed mantle. 



Plate II. 



Poromya, 1, 1*, and the beautiful pearly Pandora, 2, 3, might be 

 included in the family of Corbulidcs. Lyonsia, 4, and Thracia, 5-10, 

 represent the Anatinida. 11-18 are Solenidce, or " Razor-shells/' 

 Solens burrow in deep holes in the sand, where they remain in a per- 

 pendicular position at a great depth befow the surface, where yet their 

 presence may be traced by the opening left. Their large muscular 

 foot enables them to take great leaps when out of the holes. 



Plate III. 



Psammobia, 1-4, and Tellina, 5-16, include some of our most beau- 

 tiful shells. The animals have a large, fleshy, curved foot, and the 

 mantle open and fringed. Their shells are provided with an external 

 ligament, and teeth on the hinge. Donax, or "Wedge," 19, 20, has 

 long, separated, fringed siphons. Besides the small external ligament, 

 properly so called, the Mactridce have a triangular pit in the hinge of 

 their shell, containing an elastic substance or spring, designed to resist 

 the action of the adductor muscles. Mactra, 21-26, ends the Plate. 



Plate IV. 



Lutraria, 1-3, is another genus of Mactrida. The Venerida, 4-16 

 and 23, or "Venus" tribe, differ from it in not having the spring- 

 holding pit. Artemis, 10, 11, is known by a large angular bend in 

 the pallial impression ; and Cytherea, 23, is distinguished from Venus 



