I917-J J- HoRNELL : Indian species of Meretrix. 171 



It also occurs sub-fossil at various places in the east coast of 

 India from Ganjam to Tuticorin. 



Below are descriptions of the two varieties which I now pro- 

 pose : — 



{a) Variety ovum (Hanley). 

 (Plate IV, figs. 1-4 ; plate V, figs. 23-26 ; plate VI, figs. 34-38). 



1845. Cyf/ierea ovum, Hanley, Pro. Zool. Sac. London, 1845, p. 21. 

 i86g. Meretrix exilis, Romer, Moiiograpliie der MolluskengntttDig I'e/i/is. 

 Linn., Band I, p. J55. 



Shell variable in form, ranging from elongate ovate to oblong, 

 not usually inflated, moderately compressed, fairly solid, equi- 

 valve, sub-equilateral, white, with or without two more or less com- 

 plete narrow divergent brown bands radiating from the umbo to 

 the ventral margin — these bands very frequent in young specimens 

 but usually suppressed in the adult; covered with a thin, dull 

 olive or yellowish grey periostracum often stained with brown ; 

 umbones centrally disposed, weak, not prominent, little curved or 

 else bent straight inwards, the latter appearance commonly empha- 

 sized by corrosion which may extend to a considerable extent around 

 each umbo ; dorsal margin on each side of umbo inclined to con- 

 vexity, thin and usually without reflected margin ; ventral margin 

 varies from convex to nearly straight, entire ; anterior side round- 

 ed ; posterior side produced rather more than the anterior, 

 sometimes sub- angular, upper margin stained exteriorly with 

 greenish grey; escutcheon ovate, sub-obsolete; interior surface 

 white, stained violet along the upper posterior margin, also fre- 

 quently along the ventral edge of the hinge plate, and sometimes 

 above the anterior adductor scar ; hinge as in the type except 

 that it is weaker, narrower and more elongate in consonance with 

 the lengthening of the entire shell ; surface of the escutcheon flat- 

 tened and not elevated along the median line as in the type; 

 pallial sinus shallow as in type. Dimensions variable, usually 

 not exceeding 43 mm. in length by 35 mm. in depth and 26 

 mm. in thickness in vigorously grown individuals; generally 

 the size is smaller and 37x30X22 mm. may be taken as a fair 

 average. 



The main points of difference between this variety and the 

 type are : (a) the more pointed outline of the posterior angle of the 

 shell ; {b) the frequent presence of radial banding ; (c) the narrower 

 and more elongated form of the hinge ; (d) the flattened surface of 

 the escutcheon as opposed to its convex form in the type, where- 

 by in the latter the edge of the shell immediately above the anterior 

 lateral dental pit in the left valve is reflected outwards as a prom- 

 inent lip. 



Dimensions. — The following table gives particulars of the 

 length and breadth of the valves in 18 individuals from 6 differ- 

 ent localities, with in addition the maximum transverse diameter 

 of the entire shell in 14 instances. The relative ratios of these 



