GASTRANA. 367 



tricose shell, as well as in the greater size of the anterior 

 cardinal tooth in the left valve, and the want of lateral 

 teeth. But all these characters exist in species of the 

 parent or typical genus. The shell of T. balaustina is 

 nearly equally convex; T. squalida and other species have 

 the anterior cardinal tooth in the left valve as large in 

 proportion to the other tooth ; and T. balthica has no 

 lateral tooth. However, as I have before remarked, there 

 are no lines of absolute demarcation between any two 

 allied genera ; and there may be as good reason for sepa- 

 rating Gastrana from Tellina, as Tapes from Venus. 



Deshayes proposed in 1845 the name of Diodonta for 

 this genus, being (it may be presumed) unaware of 

 Schumacher's publication, which bears the date of 1817. 

 The one selected a European, and the other tropical 

 types ; but all are congeneric. 



Gastrana fra'gilis *, Linne. 



Tellina frag His, Linn. Syst. Nat. p. 1117. Diodonta fragilis, F. & H. i. 

 p. 284, pi. xxi. f. 3, and (animal) pi. K. f. 2. 



Body yellowish- white : tubes almost twice as long as the 

 shell is broad, one having eight and the other six rays or 

 points at their orifices ; alimentary tnbe sheathed at its base 

 foot rather large (Deshayes). 



Shell triangular, considerably produced at the posterior 

 end, more convex towards the beaks, rather thin but opaque, 

 somewhat glossy when young but afterwards becoming lustre- 

 less : sculpture, more or less irregular, thin, concentric ridges 

 or laniinse, which are slightly imbricated on the posterior side, 

 besides numerous minute and close-set parallel strise in the 

 interstices of the ridges ; the whole surface is also covered 

 with fine longitudinal striae which radiate from the beaks, and 

 are three times as many as the transverse ridges, but very 

 much more slight and scarcely raised ; where these cross the 

 ridges the crests of the latter are indistinctly beaded: colour 



* Brittle. 



