igi/.] J. HORNELL : Indian species at Meretrix. 163 



1864. Cytliei-ea zouaria. Reeve, ibid., pi. iii, figs, qa and b. 



i86g. ,, meretrix var. zouaria, Romer, Mo)iog. der Molliiskengatt. 



Venus, Band I, sub-gen. Cytlierea, pi. viii, 

 fig. le. {noil Komer' s gyaphictj, which I consider 

 to pertain to the type form). 



Lamarck's zonaria and graphica intergrade to such an extent 

 that it is often impossible to differentiate between them, hence as 

 they are at best merely colour varieties they are better merged 

 into a single group. The main characteristic is that the more 

 conspicuous markings form a zonal pattern characteristically of 

 concentric rows of zig-zag lines, or more rarely, and this only in 

 immature individuals, of concentric brown bands often broken 

 and incomplete. In all cases these markings tend to be suppressed 

 with increasing age. 



(/) Variety morphina (Lamarck). 

 (Plate IV, figs. 5-8.) 



1835. Cytlierea morphina, Lamarck (in partj, Auim. sans. Vert., 2nd ed., 



Vol, VI, p. 300. 

 1864. 7 Cytlierea morphina, Reeve, Conch. Icon., XI\', Cytherea, pi. i\-, 



fig. 12. 

 1869. Meretrix meretrix var. ?norphiiia. Romer, Monog. der Molliiskengatt. 



Venus, Band I, pi. viii, fig. i^. 



This is, I consider, a variety so indefinite in its markings 

 that it might well be suppressed, and included under the type 

 form. However, as its main character, which I consider to be the 

 presence of two narrow divergent dark radial bands extending 

 from the umbo to the ventral edge, is sometimes distinctly shown, 

 I retain it for convenience to include all shells marked more or less 

 clearly with two radial bands of dark colour. As the posterior 

 margin (vulva) of the shell is sometimes darkly tinted , the shell 

 then appears to be marked in a triradiate manner, which explains 

 why Lamarck put Venus triradiata, Gmelin, as probably synonym- 

 ous. Usually the ground colour of this shell when denuded of its 

 periostracum is either pale or dark grey, but occasionally the shell 

 is tinted yellowish or orange pink and such shells agree fairly 

 well with Reeve's description : " ash white and orange flesh colour 

 radiately tinged with violet, especially on the posterior side." 

 Strangely enough Romer considered Reeve's morphina to belong 

 to var. graphica which in the absence of zig-zag markings would 

 cause confusion. 



2. Meretrix attenuata, Dunker. 



1858. Meretrix attenuata, Dunker, Beschreibung und Abbildung neuer 



oder ivenig gekannter Meeres-Conchylien, 

 p. 53, t. xvii, figs. 7-9. 



1869. ,, ,, Romer, Monog. der Molluskengattung Venus, 



Band I, sub-gen. Cytherea, p. 36, t. x, fig. 4. 



The two specimens (Nos. 4865 and M. 10833/2 of the Indian 

 Museum collection) from the Nicobar Islands, and the larger one 



