168 CEYLON PEAKL OYSTER REPORT. 



Aripu Reefs. Six males, 29, 26, 24, 20, 18 and 17 millims. ; four females, 16, 15, 

 15 and 13 millims. 



Galle Lagoon. Two females, 32 and 29 millims. 



Galle, from cavity beneath Polyzoan crust. One female, 33 millims. 



Off Mutwal Island, 10 to 14 fathoms. One female, 38 millims. ; two males, 34 

 and 27 millims. 



From the above list of captures it will be seen that this species is a very common 

 one in Ceylon. In all, 33 specimens were captured, 19 of which were males ranging 

 from 16 millims. to 34 raillims. in length, and 13 females of from 13 millims. to 

 46 millims. in length. In no case did the depth of water over the ground on which 

 they were taken exceed 24 fathoms. LANCHESTER (1902) in a survey of G. chiragra 

 and the allied forms G. glabrous and G. graphurus expresses the opinion that the 

 two latter species are in reality only varieties of the type species of the genus, and 

 figures a series of telsons in support of this view, at the same time defining under 

 separate varietal denominations a series of types leading from G. chiragra through 

 G. glabrous to G. graphurus. The material in the present collection is by no means 

 sufficient to attempt a discussion on the point raised by LANCHESTER, but its very 

 uniformity has led me, at least for the present, to regard G. glabrous as a species 

 distinct from G. chiragra, and constantly distinguished from the latter by the 

 presence of two extra carinse on the telson. 



In only one specimen (not included in the above list of records, but referred to 

 below) was any striking divergence in the form of the telson from that of the type to be 

 noticed, and although it falls within one of the new varieties proposed by LANCHESTER, 

 I regard it not as a definite varietal form, but as an individual abnormality. 



It is true that the 33 specimens recorded above vary slightly among themselves in 

 the relative tumidity of the carinae of the telson, and in the absence from one or 

 other of them of the terminal spines. But the difference between the extremes is at 

 most slight, and the variation in any single instance (not even including the 

 abnormality noted below) is not at all such as to cause any doubt for a single 

 moment as to the validity of the specific separation of G. glabrous from G. chiragra. 



LANCHESTER (1902) also notes on the telson of G. glabrous and G. graphurus the 

 presence of two tubercles just beyond the distal end of the median cariiia. These 

 two tubercles are present in all the Ceylon specimens, and also in BROOKS' type which 

 I have examined at the British Museum. 



A note on the colour of the Ceylon examples may be of interest. Several of the 

 labels in the bottles had notes to the effect that the specimens contained therein 

 were a vivid green colour when alive, and, indeed, a general bright green coloration 

 seems to be the prevailing one in most of the specimens in the collection, many of which 

 after three years' preservation still show strong evidence of this fact. All the 

 specimens which appear to have been a uniform green when alive have four sharply 

 defined though quite small dark green pigment spots, two on the sixth abdominal 



