TELLINID2E. 333 



and at the other for the passage of a tube formed of two syphons 

 united together. This curious shell, various species of which are 

 represented in PL. XIX., are known as razor-fish, sabre-fish, and other 

 names, which in some respects indicate the peculiar form of the shell, 

 as well as its sharpness. 



The Tellinidse, the sixth family in our table, is very important, as 

 including a vast number of genera and species, of which, as types, we 

 will particularise Tellina and Donax; but Galatea, Mesodesma, 

 Semele, Sanguinolaria, Psammobia, and Capsula, are important 

 genera. 



Along the shores of the Channel and in the Mediterranean there 

 are few bivalves more abundant than the several species of the genus 

 Donax. They live near the shore in shallow water, burying them- 

 selves perpendicularly in the sand. They have the very singular 

 habit, considering their apparent helplessness, of being able to leap 

 to a certain height and then project themselves ten or twelve inches. 

 This may often be witnessed in the case of individuals left by the 

 retreating tide. If seized by the hand, and attempts are made to 

 disengage them from the sand, they continue to impress on their shell 

 a sudden and energetic movement, aided by the elasticity of their foot, 

 which is at once decisive and angular. 



Fig. 136. Donax rugosus (Linnaeus). Fig. 137. Donax denticulatus. 



The shell of the Donax is nearly triangular in shape, compressed, 

 longer than it is high, regular, equivalve, not equilateral ; the hinge 

 with three or four teeth on each valve. 



The animal is slightly compressed, and more or less triangular. Its 

 mantle, which forms two symmetrical lobes enveloping the body, is 

 open pretty nearly in all its extent, but it is united posteriorly, and 

 terminates in two syphons or nearly equal tubes, as in Fig. 130, 

 p. 326. One of these tubes serves the purpose of respiration : it is the 

 bronchial syplwn. The other, serving the purpose of ejecting the 



