36 SPOLIA ZEYLANICA. 



Length. Height. Remarks. 



3 . . 150 . . 139 . . An encysted Nematode worm* 



observed ; one very small pearl 

 in left mantle. 



4 .. 166 .. 150 .. Two small pearls in right mantle, 



one in left. 



5 . . 156 . . 135 . . ' Two Copepods present, and a 



mmute pearl in cacli mantle. 



6 .. 136 .. 117 .. Many liver parasites, but no 



pearls were found. 



With reference to the above, it is to be noted that the standard 

 height, 5| inches, is equivalent to 139 mm., and according to Mr. 

 Hornell's calculations, based upon observations extending over the 

 years 1902-1905, represents an age of about two years. 



Station II. — Across the river opposite to preceding ; bottom con- 

 sisting of a mixture of sand and mud. The search yielded one living 

 placuna, length 117 mm., height 94 mm. When held up to the light 

 the shell was sufficiently transparent to allou- the beating of the heart 

 to be seen ; some time after removal from water the heart stopped, 

 commencing again after being returned to the water. Fish spawn 

 (goby eggs) and small dome-shaped, sand-encrusted Gastropod egg- 

 capsules, from one of which I liberated 15 operculate veligers, were 

 attached to the right valve. In the normal prone position of the 

 window-pane oyster the flat right valve is uppermost, the shell 

 resting upon the convex left valve as with the edible oyster, which of 

 course adheres to the surface upon which it settles, placuna being 

 free. When the creature is breathing and feeding, these two func- 

 tions being performed simultaneously as in all lamellibranchiate 

 mollusca, the right valve is raised slightly like a lid, usually about 

 a quarter of an inch or less above the level of the left valve. If the 

 thin blade of a knife be inserted between the gaping valves, touching 

 the sensitive ed^e of the mantle, they will instantly close, and the 

 entire shell can then be lifted out of the water holding on to the 

 blade. Both large and small specimens retain this grip for many 

 days under artificial conditions. 



Station III. — On the western side of the above-mentioned man- 

 grove eyot no placunae were found. 



Station IV. — A short distance up river off the left bank, where there 

 were some remnants of last year's takings. Found only two dead 

 mud-buried placunae with mud between the valves ; height of the 

 shells about 5 inches. 



Station V. — In the Irattamaddikkali-odai (so-called on account of 

 the abundance of an edible cockle " Irattamaddi, blood-cockle," 



* Mr. Hornell recorded the presence of Ckeiracanthus uncinatiis encysted 

 vvitliiji the adductor muscle of Placuna. 



