liADULA. 557 



beaks separated by a rbomboidal area, eared on each side. 

 Ligament on each side of a strong cartilage placed in a 

 triangular pit under the beaks. Muscular scar eccentric ; 

 pallial line entire. 



S//n. Lima, Brug. Liinaria, Link. Glaucion, Oken. 



Ex. R, inflata, Chemnitz, pi. 128, fig 1. Shell, L. lima, 

 Linnceus, fig. 1, a, 1, b. 



In this genus the valves of all the species are white 

 or colourless, and the substance of the shell is composed 

 of plicate lamellae externally, and with a network of 

 minute tubuli in the inner layer. Some are covered with 

 a thin brown epidermis. Some species are peculiar to 

 northern seas ; a few are inhabitants of our own coasts ; 

 and others are found in America and the West Indies. 

 The animals swim freely about, like the Pectens, by 

 flapping their valves ; and sometimes they spin a byssus, 

 and even form a sort of nest, by weaving fragments of 

 coral and shell into their byssus, in which they live 

 gregariously. 



Species of Radula. 



Caribrea, D'Orh. paucicostata, Sow. 



lima, Linn. vulgaris, Link. . 



multicostata, Sow. 



Sub-gen. ctenoides, Klein. 



Shell thin, sub-equilateral, hardly gaping posteriorly; ribs 

 divaricate, meeting in the centre. Hinge margin nearly straight. 



scabra, Born. tenera, Chem. 



VOL. II. 4 C 



