1917] J- HoRNELL : Indian species of Mereirix. 173 



(6) Variety satparaensis (Preston). 

 (Plate V, figs. 19-21 ; plate VI, figs. 27-29). 



1914. Coi'biciila (Veloi'ita) satparaensis, Preston, Rec. Ind. Miis., X, p. 306. 



Preston's description above cited is sufficient!}^ accurate for 

 the fully grown shell. Between this and the young form of about 

 25 mm. in length, where individuality^ as a variety is lost in iden- 

 tity with the type, there is a perfect series of gradations ; advan- 

 cing from the earl}'^ stage at which divergence begins we see the 

 type form gradually altering in the ratio of length to breadth. 

 With rapid increase in stoutness, the shell assumes a shorter and 

 deeper form, the valves become highl}' convex or rather humped 

 and the umbones strongly beaked, altering completely the general 

 appearance. 



Dimensions. — The largest valve I have seen is a water-worn 

 one from False Point, Orissa (No. M. 10845/2 Ind. Mus.). This 

 measures 57^X53 mm., giving a ratio of 100 to 92*15. Another 

 particularly large one I obtained from the Surla shell-pits in 

 Ganjam. This measures 57 mm. long by over 50 mm. deep, equi- 

 valent to the ratio of 100 to 8772 (deposited in the Calcutta 

 Museum). Five other shells from Korampalam shell-pits, Tuti- 

 corin, with their valves undisplaced, measured : — 



Millimetres. Respective Ratios. 



39X38X30J =i(jo to 97-44 to 78-21 



38fX36fX3o =100 to 94-84 to 77-42 



31x29^x23^ =100 to 95-97 to 75-00 



30^X27! X22| =100 to gi-74 to 74-38 



43X4o|-X32 =100 to 94-19 to 74-42 



Average of Ratios =100 to 94-84 to 75-89 



Localities. — This variety is common everywhere in the shell 

 deposits of sub-fossil age on the borders of Chilka Lake, Sonapur 

 backwater (Ganjam), Pulicat Lake and Sadras backwater (Chingle- 

 put) ; in shell-pits in the Mandapam Peninsula (Ramnad district) 

 and also at Korampalam near Tuticorin ; a water-worn valve from 

 False Point, Orissa. 



Variety satparaensis is found only in the sub-fossil condition ; 

 no living individuals appear to assume this excessively stout form. 

 This would seem to indicate that the conditions favouring an ex- 

 tremely rapid deposit of lime salts have deteriorated appreciably 

 since the time the sub-fossil deposits were formed, or that the 

 variety had found it a disadvantage to be possessed of special 

 abilit\' to secrete large quantities of lime in its shells. 



