EXPLANATION OF PLATE VII. 



Meretrix meretrix var. impudica (Chemn.), 



Figs. 39 and 40. — Outer and inner view of left valve. The former 

 shows the coarse chevron marks upon the umbo so character- 

 istic of this variety. The margin of the vulva does not show 

 in this photograph. The inner view is to show the charac- 

 teristic shallow form of the pallial sinus in Meretrix meretrix 

 as distinct from the deep sinus of M . attenuata and M . lusoria. 



Meretrix attenuata var. fiava, var, nov. 



Figs. 41 and 42. — From the Nicobar Islands. No. 4865 of the 

 Indian Museum collection. Note the total absence of the 

 characteristic chevron markings described by Dunker and 

 Romer. 



Meretrix lusoria (Chemn.). 



Fig. 43. — A left valve from Japan. This shell is occasionally more 

 elongated posteriorly than in this specimen and this causes 

 the pallial sinus to be less open than in the latter, where it is 

 characteristically almost semi-circular in outline. 



All the figures are natural size. 



