EXPLANATION OF PLATE VL 



■ Meretrix casta var. salparaensis (Preston). 



Figs. 27 to 29. — All from Korampalam, Tuticorin. Fig 29 is a 

 transition form to the true casta, the hinge being weaker than 

 normal, but with the umbo typically hooded. 



Meretrix casta (Chemnitz). Type. 



Figs. 30 and 31 are very typical, with heavy hinge and short 

 cordate outline ; the second is the more common form and 

 shows some tendency to elongation posteriorly. (Fig. 30 is 

 from Tuticorin, 31 from Pulicat). 



Figs. 32 and 33 (Pulicat and Ennur) show more emphatic elonga- 

 tion posteriorly and in fig. ^^ we have a form approaching the 

 ovum form such as is seen in fig. 34. 



Meretrix casta var. ovum (Hanley). 



Figs. 34 to 38 show part of the range in shape shown by this very 

 variable variety, extending from the comparatively short stout 

 form of fig. 34, to the narrow elongated form of fig. 38. Com- 

 pare with figs 23 to 26, pi. V. All from Tellicherry except 

 fig. 38, from Mahe, Malabar. 



Figs. 27-38316 all inner views of the riuht valve in M. casta and its two 

 varieties, showing the great range in variation exhibited by these shells and 

 the gradations linking together these three main forms. 



All the figures are natural size. 



