398 CEYLON PEARL OYSTER REPORT. 



and there is a suggestion of its continuance anteriorly below the orbit to the antero- 

 external angle of the buccal cavern. It is divided by grooves into four sufficiently 

 distinct, but little-prominent, lobes ; the groove between the 1st and 2nd lobe is the 

 least distinct. 



Under surface of carapace smooth and polished, and tabulated as dorsal surface. 

 A distinct groove runs obliquely backward from the region of the green gland 

 aperture, to end at the border of the carapace just above the base of walking leg 4. 

 There is a patch of hair above the base of the chelipeds, and a fringe follows the edge 

 of the carapace above the bases of the walking legs, and skirts abdomen. 



Thoracic sternal region is in its exposed portion broken by transverse pubescent 

 grooves into regions appropriate to the segments bearing chelipeds and four walking 

 legs. There is some tendency to subdivision of these regions (see figure), and the 

 surfaces are polished and show some dimples. 



Abdomen. The seven abdominal terga are separate. Tergum VI. is about twice 

 as long as any of the first five (which are subequal in length) and of approximately 

 the same length as tergum VII. In addition to a little dimpling, each tergum is 

 traversed by a pubescent transverse groove, before and behind which, in the case of 

 VI., is a slightly marked additional groove. The abdomen is well fringed with hair. 



Antennules fold obliquely making an angle of 40 (approximately) with a 

 horizontal line. 



Antennse. Basal antennal segment, as a whole, falls short of the inner orbital 

 angles ; its outer angle, however, is produced into the hiatus ; its inner angle touches 

 a downgrowth of the front. The orbital hiatus thus remains open for the most part, 

 and in it is seen the short antennal flagellum (flagellum length -i- C.I. = O'll). 



External Maxillipeds. See figure. The merus is of approximately the same breadth 

 as the ischium and about one half as long ; it is pointed anteriorly, its borders sloping 

 obliquely backwards and making together an angle of 90 approximately. The 

 flagellum arises from the inner side of the apex. A longitudinal groove traverses 

 both merus and ischium. The surface of the external maxilliped is polished. 



Chelipeds of equal size. The upper, outer, and under surfaces of the arm, wrist, 

 and hand are subdivided by pubescent grooves into polished lobes somewhat 

 reminiscent of brain convolutions. The inner surface of the arm is smooth, and is 

 concave in correlation with the convex under surface of the carapace ; on the sharp 

 inner border of the merus are three blunt teeth (exclusive of the distal angle), the 

 same border has a fringe of hair ; the upper border is also sharp ; the inner border is 

 well rounded. The length and breadth of the upper surface of the wrist are equal, 

 its inner anterior angle is produced into a tooth, to the inner side of which is a much 

 smaller one ; the upper and outer surfaces form a continuous curve. The upper border 

 of the hand is armed with a row of six or seven blunt teeth, or tubercles (six on right 

 hand, seven on left hand) ; the grooves of the hand, transverse in the main, are crossed 

 by two which are longitudinal (one running to the outer side of the base of the dactylus, 



