378 CEYLON PEARL OYSTER REPORT. 



extremities toothed ; anterior extremity broad and obliquely rounded, posterior 

 narrower, rounded off below, and obscurely angulated above ; dorsal margin sinuated 

 in the centre, highest in front and sloping towards the posterior, ventral sinuated in 

 the middle ; seen from above pear-shaped, greatest width near the posterior end, 

 and equal to more than half the length, the outline between the widest point and 

 the anterior end shows two distinct constrictions ; shell surface marked with coarse 

 impressed puncta ; each valve seen from the side shows two distinct grooves ; size, 

 0'56 millim. 



In the general washings and in washings from Cheval pearl oysters. 



Named after Captain ROBERT KNOX, 20 years a captive in Ceylon in the 

 seventeenth century. 



Cythere chalmersi, n. sp. Plate II., figs. 11 and 12. 



Shell seen from the side subsigmoid, height equal to half the length, extremities 

 corrugated but not toothed ; anterior extremity very obliquely rounded, posterior 

 narrower, and broadly rounded ; dorsal margin highest at the anterior end, nearly 

 flat, with a gentle slope towards the posterior ; ventral sinuated in the middle ; seen 

 from above pear-shaped, outline irregular, and marked by three constrictions, widest 

 near the posterior end, greatest width equal to about half the length ; anterior and 

 posterior ends with strong thickened lips, the posterior forming a distinct pro- 

 tuberance ; surface of the shell marked with moderately coarse impressed puncta, 

 and near the extremities with a row of circular depressions ; seen from the side, the 

 valves show three distinct grooves ; size, 0'7 millim. 



In the general washings and in washings from Gulf of Manaar sponges. 



Named after Dr. A. J. CHALMERS, Professor in the Medical College, Colombo. 



Cythere imthurni, n. sp. Plate II., figs. 13 and 14. 



Shell seen from the side oblong, subquadrangular, height slightly less than halt 

 the length ; extremities smooth, anterior extremely broad and obliquely rounded, 

 with an internal row of subcircular markings ; posterior narrower, rounded above and 

 truncate below ; dorsal margin highest at the anterior end, nearly flat, with a gentle 

 slope towards the posterior, ventral deeply sinuated near the middle ; seen from 

 above rather wedge shaped, with nearly parallel sides, deeply constricted near the 

 posterior end, length about two and a half times the width ; anterior margin 

 acuminate with projecting thickened lips, posterior almost truncated, projecting 

 slightly in the centre ; surface of the shell marked with large irregular impressed 

 puncta, and, when viewed from the side, with a deep hollow near the posterior ; 

 size, 0'5 millim. 



In the general washings, in washings from Cheval pearl oysters, and from Gulf of 

 Manaar sponges. 



Named after the Honourable E. F. IM THURN, Lieutenant-Governor of Ceylon 

 during the pearl oyster investigation in 1902. 



