388 



CEYLON PEARL OYSTER REPORT. 



In the young male (e) the median lobe of the rostrum is reduced to a declivous 

 denticle of approximately the same length as the denticular lateral lobes, which are 

 in this example more strongly developed than usual. Considerable growth -changes 

 in cheliped length for males are indicated by the measurements given above. 



Lambrus (Platylambrus) carinatus, H. M.-Eow., 1834 A.1, p. 263. 



Localities : Coral reefs, Gulf of Manaar, four specimens ; off Mutwal Island, one 

 specimen ; pearl banks, Gulf of Manaar, nine specimens. 



Description: The specimens include four ovigerous females (incl. f-h), six non- 

 ovigerous females (incl. a-e), and four adult males. 



Some characters exhibit high variability : 



(1) The mid-dorsal teeth may be large and laterally compressed, or they may be 

 smaller and peg-like. In one example the most anterior of the three is obsolescent. 



(2) The branchial ridges vary in number and in character. There may be on each 

 side a single sharp carina, a single granular ridge, a pair of granular ridges, or a pair 

 of smooth ridges ; the second ridge may be very inconspicuous, and there may be a 

 granule or two in the middle of such a faint ridge. 



(3) The carapace may be free from granules, or granules may be present, but 

 confined to the depression on either side of the cardiac region, or a few may extend 

 over the branchial region also. 



Remarks. I include Lambrus holdsworthi, MIERS, as a synonym. A. MILNE- 

 EDWARDS' brief diagnosis of L. carinatus applies to MIERS' " type "-specimens of 

 L. holdsworthi in the British Museum. Some of my specimens, which I group as 

 var. holdsworthi, agree with the latter ; others agree with ALCOCK' s description of 

 his examples of L. carinatus I call these var. alcocki. 



In var. alcocki there is a single carinate ridge on each branchial region ; in var. 

 holdsworthi there are two low granular ridges. 



In var. alcocki the mid-dorsal tubercles are more prominent and are laterally 

 compressed ; in var. holdsworthi they are more peg-like and less prominent. 



In var. alcocki the carapace tends to be free from granules ; a fair number of 

 granules are present in var. holdsworthi, 



The variations presented by the present forms in regard to median dorsal teeth and 

 branchial ridges which I have referred to above minimise or break down two of 

 the distinctions which ALCOCK draws between his specimens of L. carinatus and of 

 L. prensor. All my specimens agree with those described by ALCOCK in the 

 character of the sub-orbital lobe (bilobed, the inner lobe rounded and not produced 



