iQiy-] J- HoRNELL : Indian species oj Meretrix. i6r 



to two short radial lines. These markings are much more conspicu- 

 ous in impudica than are the umbonar dots and rayed marks of 

 the type. Fig. 39 shows a well-marked example of the zone 

 pattern, while in fig. 18 we have a rare combination of the impu- 

 dica colour scheme of clearly defined vulva with the discontinuous 

 rayed blotching seen frequently in var. morphina. Young indivi- 

 duals of 15 to 18 mm. in length are frequently much decorated 

 with dark chevron markings, such as are depicted in figs. 14 to 17, 

 pi. V. Such conspicuously marked individuals are common in the 

 outer channel of the Chilka Lake. They were incorrectly identi- 

 fied as M . ovum by Preston. 



Localities. — Common in the outer channel^ Chilka Lake 

 {Annandale and Kemp) ; in the sands immediately within the 

 mouth of Silavathurai lagoon^ Tuticorin, and in the delta of the 

 Tambraparni, Tinnevelly district (/. H.). A sub-fossil valve from 

 Surla shell-pits, Ganjam. Also Tavoy (Burma), Arakan, Trinco- 

 malie (Ceylon), Bombay and ? Andaman Islands; all in the Indian 

 Museum collection. 



DimeMsions. — The largest Chilka specimen measures 65x57^ 

 X40 mm., while the largest of the Tuticorin ones is 74X64 

 X 40 mm. 



(c) Variety castanea (Lamarck). 



(Plate IV, fig. 12.) 



1835. Cvtlicrea castanea, Lamarck, Aiinii. sans. I'erf., 2nd ed., X'ol. \'l, 



p. 299. 

 1906. Mei'etri.x castanea, Standen and Leicester in Ceylon Pearl Oyster 



Fisheries, Pt. V, p. 293. 



Distinguished from all other varieties by its uniform brown 

 or chestnut colouration ; the vulva is not sharply demarcated, 

 but the colouring in this region is usually darker than over the 

 rest of the shell. There are no definite umbonar markings to be 

 made out. On some shells an obscure and irregular zoning can be 

 observed due to some of the growth zones being darker in tint 

 than adjoining ones. 



This is a well-marked variety seemingly of rare occurrence as 

 I have found a single specimen onl}^ at Tuticorin and another in 

 the Tambraparni delta, while out of the whole Indian Museum 

 collection of Meretrix, nine only are of this colouration. Of these 

 latter two (No. 4788) are labelled Indian Ocean, one is included in 

 a collection of 11 shells (M. 398) from the Tavoy Coast, Burma, 

 another (M. 10836/2) is from Bombay, while so many as five 

 (M. 10842/2) are from Tf incomalie, Ceylon. Standen and Leicester 

 also report this variety from Trincomalie and Tarhpalakam , so 

 it would appear to be relatively more abundant there than in any 

 other locality. Reeve records it from China and the Philippine 

 Islands. 



Dimensions. — The largest individual seen (Ind. Mus. coll. 

 No. 4788) measures 68 X 61 x 42^ mm. Five other large specimens 

 measure respectively : — 



