252 CEYLON PEARL OYSTER REPORT. 



Head of an unusual form in this genus, the lower antennae originating immediately 

 below the upper with a weil-detined but rounded lateral angle. Eyes scarcely 

 discernible (fig. 13. a). 



Third pleon segment with the hind margin slightly convex, the lower margin 

 straight till turned up to meet the slightly produced angle (fig. 13. pi. 3 ). 



First segment of the urus with a small carina. 



Antennae short, the lower rather the longer, reaching the end of the 2nd 

 mesosome segment. First joint of the upper about twice as long and as thick 

 again as the 2nd ; 3rd not distinguishable from the flagellum, which is 5-jointed 

 without the above doubtful joint, with a long terminal seta. The lower have 

 the first 2 joints subequal, the 3rd the longest, with 5 spines on the lower 

 margin. 



Gnathopods normal. 



First and 2nd perseopods of the usual form, the dactylus about as long as the 

 2 preceding joints. 



Third and 4th peraeopods : 1st joint fully as wide as long ; 4th joint has the 

 posterior longitudinal half produced downwards for two-thirds of the length of the 5th 

 joint, terminating in 2 long, unequal serrate spines. In the 4 th pair the dactylus is 

 rudimentary (fig. 13. pp.*). 



Fifth perseopods : 1st joint with the front margin longer than the remaining 

 joints ; it is concave on the upper and convex on the lower part ; the hind margin 

 evenly convex, reaching downwards to the 5th joint ; about 9 simple unequal seta? 

 and 4 or 5 setules on the lower part ; 2nd joint longer than any of the succeeding, 

 4th, 5th, and 6th subequal, the last lanceolate, acute. None of the joints have their 

 'angles materially produced (fig. 13. pp. 5 ). 



First uropods : peduncles almost twice as long as the subequal rami ; 2 spinous 

 and finely pectinate ridges on their upper sides ; rami curved, unarmed, except a 

 spine near the base of the inner. 



Second uropods : peduncles rather longer than the subequal rami, sparsely spinous ; 

 rami straight, 5 spines on the inner margin of the inner (fig. 13. ur.). 



Third uropods : rami rather longer than the peduncles, the outer having the outer 

 margin very convex, the distal half beautifully ornamented with a double row of 

 minute spines ; the inner margins straight with a few long setae ; inner rami 

 concealed by the outer apparently as long and wide as these with long and dense 

 seta? at the tips (fig. 13. ur.). 



Telson divided about three-fourths of its length, with long upright setae along the 

 margins of the cleft. 



Length 4 - 5 millims. 



Easily recognisable by the short antennae, the peculiar structure of the 4th joints 

 of the 3rd and 4th and the 1st joint of the 5th peraeopods, and the curiously formed 

 and ornamented 3rd uropods. 



