380 CEYLON PEARL OYSTER REPORT. 



antero-external angle of the buccal cavern is produced as a petaloid projection ; on the 

 pterygostomial ridge running obliquely backward from this there are two tubercles, 

 and a third still further back just above the base of the cheliped. 



The chelipeds are rather more slender than the walking legs. Ch.l. -i-C.l. = 0*91. 

 The dactylopodites of the walking legs are roughened, hardly denticulate, on their 

 lower borders. Carapace length is 875. 



The general form of the carapace and of the rostral spines, together with the slight 

 epibranchial tubercle, suggest alliance with the H. convexus group. The small but 

 distinct supra-ocular tooth is interesting. It occurs in H. agassizi ; in H. pehlevi 

 there is no isolated tooth, but the lower half of the upper anterior border of the large 

 post-ocular tooth bears a smaller tooth, which is perhaps its representative. At all 

 events, the two examples of H. irami enable one to make a very pretty series ; in 

 specimen (a) there is on the right an isolated supra-orbital tooth well separated from 

 both supra-ocular eave and large post-ocular tooth, on the left side it is at the base of 

 the latter, though distinct from it, in (b) it is on either side hardly separated from the 

 post-ocular tooth and might be described as situated upon it : this leads to the 

 condition seen in H. pehlevi. 



For purposes of key this new species comes under section II.2.ii.&. of ALCOCK'S 

 arrangement (A.I, p. 208) with H. planasius; from the latter it is easily to be 

 distinguished by its supra- ocular tooth. 



The male example of the new species is of interest as exhibiting a condition of 

 abdomen and chelipeds evidently due to the presence of the parasitic Sacculina. The 

 chelipeds are much as in the female, the abdomen is much broadened, resembling that 

 of a half-grown female ; the larger pair of copulatory appendages reach back about 

 half way along the abdomen. 



Naxia investigatoris, ALCOCK, 1895 A.I, p. 218 ; A.Invest., pi. xxi., fig. 6. 



Localities : Coral reefs, Gulf of Manaar, one specimen (ovigerous ? ) ; pearl banks, 

 Gulf of Manaar, one specimen (ovigerous ? ) ; off Mutwal Island, one specimen (<? ). 



Description: C.I. Rost.sp.l.-rC.l. Ch.L-rC.l. 



(a) ovigerous ? . . . 16 '00 0'25 TOO 



(c) adult <? 16-00 0-37 1'19 



The present male example suggests that facultative dimorphism occurs in the 

 species. It has a well-grown appearance. In spite of its "non-breeding" type of 

 cheliped, it is larger than a male specimen of ALCOCK'S in the British Museum, which 

 has chelipeds of " breeding" type ; it is perhaps a " middle " male. 



Naxia hirta (A. MILNE-EDWARDS), 1865 A.1, p. 218. 



Localities : Aripu coral reefs, Gulf of Manaar, nine specimens ; Chilaw Paar, one 

 specimen ; pearl banks, Gulf of Manaar, seven specimens ; off Mutwal Island, two 

 specimens. 



