EXPLANATION OF PLATE IV. 



Photographs of valves of the two Indian species of Meretrix 

 to show the frequency and the range of radial colour banding. 



Meretrix casta var. ovum (Hanley). 



Figs, i and 2. — Two examples from Tellicherry with two narrow 

 and widely separated rays. (These do not show clearly in the 

 photographs.) 



Fig. 3. — A small shell from the same localitj^ showing two strong 

 widening ra^^s, a common type among young individuals of 

 this variety. 



Fig. 4.— a half-grown specimen showing two strong rays, which in 

 the umbonai region have coarse chevron-shaped marks super- 

 added. Baliapatam River, Malabar. 



Meretrix meretrix var. morphina (Lmk.). 



Figs. 5, 6, 7 and 8. — Four valves showing the wide variations in 

 the typical colour scheme of two radial bands widening as 

 they pass away from the umbo. 



Fig. 5 is the most perfect, the two bands strongly marked throughout 

 their course, and with the umbo conspicuously marked with linear brown 

 markings more or less chevroned. 



Figs. 6 and 7 approach the pattern form of No. 5, but here the radii are 

 discontinuous and strong only upon the umbones, where both show chevron - 

 spotting superadded. Tuticorin. 



Fig. 8. A typical valve from Tuticorin showing the modification of the 

 rays found in fully adult individuals. Here the rays are discontinuous, blotchy 

 and obscure, buried partly within the shell substance and showing chiefly as 

 two dark clouded areas close to the anterior and posterior angles of the ventral 

 margin. (These areas do not show well in the photograph). 



Meretrix meretrix var. aurora , var. nov. 



Figs. 9, 10 and 11. — Three shells from Tellicherry showing the 

 multiple raying characteristic of this variety. 



Meretrix meretrix var. castanea (Lmk.). 



Fig, 12. — A typical specimen from the Tambraparni delta, Tin- 

 nevelly. 



All the figures are natural size. 



