63 



CHAPTER XII. 



OF THE DONAX. GENUS IX. 



DONAX. 



"Animal a Tet/ij/s. Shell bivalve, the fore part of the margin very obtuse ; 

 hinge with two teeth, and a single marginal tooth a little distant be- 

 hind." — Linn. 



1 HIS is a very indistinct genus, being in some instances diffi- 

 cult to distinguish from the Venus, and in other cases from 

 the Tellina, between which it seems to form a connecting 

 link, the Donax scripta agreeing in the teeth with Venus 

 MeriJe, as D. Truncvhis does with some of the Tellince. 



Many species are truncate at one end or wedge-shaped ; 

 but this cannot be considered the essential character, as some 

 species are not so, and some shells of other genera are wedge- 

 shaped also, as Mactra stiiahda, &c. 



The centre teeth vary in mimber in the difl^rent species ; 

 some have only one in each valve, as D. radiata ; some have 

 one in one valve and two in the other, as D. Icevigata, Trun- 

 culiis, &c. ; and others lia\ e two in one valve and three in 

 the other, as D. scripta, &c. The lateral teeth also vary, 

 some shells having none, as D. Trnnciili(s, Icevigata, &c. ; some 

 have them on one side, as D. scripta ; and some have them 

 On both sides, as jD. denticniata, &c. 



The cartilage is external ; in some species it is prominent, 



