DONAX WEDGE SHELL. 167 



adopted either as indicative of the sagittate form, 

 or of the rapidity with which, in consequence of 

 its peculiar shape, the animal can dart into the 

 sand, whenever danger threatens. One species 

 (Donax Irus) perforates the hardest limestone, 

 but by what means it effects a lodgment in such 

 a substance, has not been ascertained ; pieces of 

 stone are often thrown ashore on the Devonshire 

 coast filled with these shells fitting into the 

 apertures which they have pierced. The shells 

 of this genus are generally of a fine rich purple 

 colour, sometimes marked with rays of purple on 

 a white ground. Many of the species are of a 

 yellow olive hue. The animal has ft two long 

 slender tubes not joined together, and a lamellar 

 foot. The Donaces are marine littoral shells. 



DONAX Denticulata. 



TOOTHED DONAX. 



Specific Character. Shell strong, thick, ovate, 

 wedge-shaped, with longitudinal striae, the in- 

 terstices punctured ; * anterior slope rough, with 

 transverse striae, and elevated in the middle in a 

 kind of keel ; white or lead colour, usually with 

 a few purple rays proceeding from the umbones, 

 inside purple ; very concave under the umbones ; 



* Punctured, pricked or marked with small dots, from the 

 Latin punctwm, a point or dot. 



