8 DR. NELSON ANNANDALE ON 



umbilicus. The outer lip at the anterior end of the mouth is very 

 slightly expanded. 



The external surface of the shell is highly polished and often 

 has a malleated appearance due to relatively large but very shallow 

 depressions arranged roughly in a spiral manner. Numerous 

 minute longitudinal striae can be detected with the aid of a 

 hand-lens. 



The external colour is pale olivaceous green, sometimes with 

 a reddish tinge. Spiral bands are absent, but irregular black long- 

 itudinal lines sometimes occur. The outer lip is sometimes black- 

 ened externally. The interior of the shell is yellowish white and 

 the periphery of the mouth is more or less infuscated. 



The operculum is thin, long and narrow, with the posterior 

 extremity pointed and slightly introverted and the anterior extremi- 

 ty narrowly rounded. The outer margin is evenly convex, the 

 inner margin rather deeply concave in its posterior half, nearly 

 straight anteriorly. The external surface is concave as a whole, the 

 internal surface slightly convex. There is a well defined ridge on 

 the inner border of the former, proceeding forwards from a 

 point a little in front of the posterior extremity and gradually grow- 

 ing broader until it reaches a point about two-thirds the distance 

 from the posterior to the anterior extremity. The lines of growth 

 are well-defined and regular and the epidermis thin and polished. 

 The muscular scar on the internal surface is large and its smooth area 

 relatively extensive. The sculpture of the border of the scar is 

 minute and irregular and does not extend outwards over the whole 

 border on the outer edge of the scar. On the inner edge the scar 

 is defiued by a prominent ridge. The nacre is of a leaden grey tint. 



The following measurements are those, with the exception 

 of the first shell, of specimens assigned by Nevill to his var. 

 compressa. I have not the materia] to decide whether either this 

 variety or Fischer and Dautzenberg's var. major is beyond the 

 limits of individual variation. 



Measurements (in millimetres) and Proportions of Shells. 



Height • 75 61 55 



Maximum diameter ... ... 60 46 41 



JOTJRN. NAT. HIST. SOC. SIAM. 



