8 4 



belong to separate species, that of Sind being charac- 

 terized by a white adductor scar, that of Madras (Pulicat 

 and Ennore as typical examples) being purplish black. 

 Both species appear to be related to the robust mud- 

 loving Portuguese oyster of European commerce 

 (O. angulata) ; like the latter the sexes in these Indian 

 species are separate. 



In the Indus creeks on the coast of Sind, no rocky 

 out-crops occur, neither pebbles nor gravel is to be found 

 anywhere. The cultch to which the oysters adhere 

 consists solely of the accumulated shells of former oyster 

 generations. In almost all cases the oyster patches occur 

 close to the low-water level of spring-tides ; usually the 

 beds are more or less uncovered at such times. The 

 oysters, nearly all dead, seen in the Sind creeks may 

 attain relatively enormous size. I have note of a dead 

 valve measuring 15 inches in length and I have seen 

 several in which the hinge region alone measured from 

 7 to 8 inches in length. When growing in muddy 

 creeks the Sind oysters are characteristically elongate, 

 long and narrow and typical " slipper-oysters." The 

 oysters in any patch tend to segregate into clusters 

 composed usually of from 5 to 12 or more individuals. 

 A very notable feature characterising the habit of growth 

 is the way the oysters in these clumps retain their own 

 individuality ; each keeps the greater part of its shell free 

 from cohesion with those of its neighbours due to a 

 slight amount of radial divergence in the direction of 

 growth among the several oysters. This habit produces 

 very serviceable clusters, readily separable into units 

 as the area of cohesion is small and limited to the 

 massive dorsal region of the valves. The joint made by 

 the adherent surfaces is also imperfect, rendered weak 

 by the muddy scum present on the older valves when 

 the younger come to attach to them. 



Similar conditions entail similar habits in the case of 

 muddy creeks and channels in estuaries and backwaters 

 on the Madras coast, but there are many localities where 

 stones and more or less consolidated and stable sandy 



