SHELL-BEARING BRITISH MOLLUSCA. Vll 



by one tooth on the hinge standing out a little way from the central 

 ones. Astarte, 17-22, belongs to the Cyprinidce, 



Plate "V, 



Fig. 1-3 also represent genera of Cyprinidce. They have no bend in 

 the palleal impression. Cardium, or "Cockle," 4-13, presents a pecu- 

 liarity in the foot, which is large and bent, and enables the animal to 

 leap in a very lively manner. The family of Lucinida occupy the re- 

 maining figures. Lucina has a curious tongue-shaped doubling of 

 the pallial impression. 



Plate VI. 



The Kelliada, 1-15, are marine, while the Cycladida, completing 

 the Plate, are fresh- water bivalves, and may be found in many ponds and 

 rivers. 



Plate VII. 



Of the Unionida, or " Fresh-water Mussels," Unio, 1-3, has teeth on 

 the hinge, and Anodon, 4, has not : it is a thin shell. The foot of these 

 molluscs is very large, and is used in cutting the animal's way through 

 the mud in which it burrows. Of the marine, or true Mussels, Modiola, 

 6-9, and Crenella, 12-17, have a portion of the shell reaching beyond 

 the point or apex, which in Mytilus is terminal, 18-21. Breissina, 5, 

 is shaped like Mytilus, but lives in fresh-water docks. The Mytilidce 

 attach themselves by means of horny threads spun from the foot, and 

 called a "byssus." 



Plate VIII. 



Shells of Arcada, 1-14, have the hinge characterized by a series of 

 teeth on each side of the apex. Nucula, Area, and Pectunculus are 

 easily distinguished. Limopsis, 14, has a spring pit between the two 

 rows. Our figure of Pinna, 16, is from a young specimen : it grows to 

 great size, and spins a very silky byssus. The shell of Anomia, 18. is 

 fixed to rocks, etc., by means of a bony button passing through a hole 

 or sinus in the lower valve. Lima, 22-24, has a light, thin shell, and 

 its mantle is adorned with beautiful fringes. It swims rapidly through 

 the water by the opening and shutting of its valves, and also has the 



