204 CEYLON PEARL OYSTER REPORT. 



The first two of these are very short and considerably narrower than the head ; 

 the third and fourth (fused) are longer and wider, and together are about three-fifths 

 the size of the carapace shield. The fifth segment is shorter and narrower than the 

 fourth. It is divided transversely into thirds, the two outer divisions extending 

 backwards in the form of wide rounded lobes on either side of the genital segment 

 and abdomen, the median division forming a shallow rounded sinus for the attach- 

 ment of the genital segment. 



The genital segment and abdomen together form a hemisphere about the size of 

 one of the posterior lobes of the fifth segment. The abdomen is one-jointed and 

 bears on its ventral surface, at the posterior margin, two large cylindrical anal 

 papillae. These are longer than the abdomen itself, and each is tipped with a claw 

 and a spine. The claw, which is on the inside, is nearly as long as the papilla, stout, 

 and abruptly curved near the tip, exactly like the prehensile claws on the second 

 antennse of the Caligidse. The spine is only one-fourth as long as the claw, and 

 straight (fig. 57). 



Egg-tubes wider than the genital segment and one-third longer than the entire 

 body ; eggs large, about 30 in each tube. 



The first antennse are five-jointed, the joints diminishing in diameter towards the 

 tip ; the setae are very scattered except on the third and last joints. The second 

 antennas have a stout and conical basal joint, and a slender, strongly-curved 

 terminal claw. 



The mouth-tube is short and wide, with a rather blunt tip, enclosing the slender 

 mandibles which are toothed on their inner margins. The second maxillse and first 

 maxillipeds are about the same size and close together at the sides of the mouth-tube. 

 Each is two-jointed, and is made up of a short and plump basal joint and a slender 

 terminal spine. The maxillipeds, of course, are rudimentary when reduced to this 

 size, and are similar to those found in Pseudoclavella, Cycnus, Cybicola, and other 

 Dichelestiids (fig. 52). 



The second maxillipeds are fairly developed and much resemble the first pair in the 

 Caligidse. They are two-jointed, the joints about the same length, the terminal one 

 tipped with a short and straight claw. 



There are only two pairs of swimming legs, both biramose, with the rami linear and 

 two-jointed. In each pair the exopod joints are about the same length, while the 

 basal joint of the endopod is much shorter than the terminal. 



Owing to the habit which the species has of lying in a burrow, the oviducts open 

 on the dorsal surface, on either side of, and quite near to, the mid-line. The ovaries 

 and the internal portions of the oviducts fill the entire thorax and even project 

 forward into the head. The external portions (egg-tubes) start out at right angles to 

 the dorsal surface, and are thus lifted well above the edge of the burrow. They then 

 curve over and lie in close contact with the surface of the fish's gill outside the 

 burrow (fig. 48). 



