382 CEYLON PEARL OYSTER REPORT. 



on either side of the posterior limit of the median longitudinal rostral groove ; these 

 and the small anterior one of the median dorsal row form a triangle ; the three are 

 sub-equal in size and are roughly one-third the size of the second member of the 

 median dorsal row. The antero-external angle of the buccal cavern is produced into 

 a tubercle, and this is the most anterior member of a row of four, of which the second 

 is on the sub-hepatic region and the third and fourth are on the lateral border of the 

 carapace. Parallel to this a row of four tubercles runs obliquely backwards and 

 outwards from the posterior angle of the orbit ; of these, the first is hepatic and the 

 rest branchial. On either side between this row and the mid-dorsal row are twelve 

 tubercles, four gastric and eight branchial'. The gastric ones are small and occupy 

 the corners of an antero-posterior oblong, of the branchial ones five follow the groove 

 separating branchial from middle regions (second and sixth well developed, rest 

 small), the remaining three lie to outer side, the posterior one being well developed, 

 and the two anterior very close together. The middle regions of the carapace are 

 separated from the lateral ones by distinct sinuous grooves ; the branchio-hepatic 

 groove also is distinct. In addition to the tubercles described above, the basal 

 antennal segment is produced into one, there is another just behind this to the 

 outer side of the opening of the green gland and just in front of the tubercle at the 

 antero-external angle of the buccal cavern, already described. The interantennulary 

 septum is produced ventrally in the middle region to form a much compressed tooth. 



The merus of the external maxilliped has a very distinct notch in the anterior part 

 of its inner border, its anterior border is oblique and a little convex, its outer angle 

 rounded and slightly produced, its exposed surface concave ; the ischium has its inner 

 border obviously dentate. The length of the buccal cavern (a straight line uniting 

 the inner base of the antero-external tubercle to the outer posterior angle) is 0*98, 

 its breadth (across region of the two antero-external tubercles) ; outer border of 

 merus -r- breadth of buccal cavern =0*48 ; outer border of ischium -i- breadth of buccal 

 cavern =0'60. 



Chelipeds slender, about the same degree of stoutness as the 2nd pair of 

 walking legs, but a good deal shorter. Ch.l.-^C.l. = 1'15. W.L.l.l.-j-C.l. = 2'37 ; 

 W.L.2.L-5-C.L = 1-98 ; W.L.3.L-7-C.1. = 1'64 ; W.L. 4.1.^0.1. = 1-37. 



Abdominal segments IV. to VI. are fused (the specimen is female), but grooves 

 representing joints remain very distinct. 



Egeria arachnoides (RuMPmus) A.1, p. 223. 



Localities : Coral reefs, Gulf of Manaar, one specimen ; south-east of Ceylon, 

 18 fathoms, one specimen. 

 Description : Males both probably immature. 



Tylocarcinus styx (HERBST), 1803 A.I, p. 235. 



Locality :- -Cheval Paar, two specimens (ovigerous ? and young ? ). 

 Description :- -C.I. of the ovigerous female = 16'5. 



