174 CEYLON PEARL OYSTER REPORT. 



ments of exopods. Telson very short, the post-anal part reduced to a spiniform 

 process tipped with two small spinules and without lateral spines. 



Paradiastylis brachyura, n. sp. Plate V., figs. 76 to 90. 



Desci-iption of sub-adult Female. Total length 3 - 2 millims. : 



Carapace inflated, a little less than one-third of the total length, its breadth about 

 three-fourths, and its depth two-thirds of its length. Pseudorostrum acute, hori- 

 zontal, the lateral plates meeting in front of the ocular lobe for a distance ecpial to 

 the width of the latter. The tip of the pseudorostrum is armed with a pair of 

 divergent spines. Antennal notch shallow. Antero-lateral angle not produced, 

 rounded, serrate. On each side of the carapace are four curved ridges running 

 obliquely from above downwards and forwards. The most anterior and strongest of 

 these is serrate, and the area in front of and above it is depressed on each side, 

 leaving a median keel. The fourth or hindmost ridge on either side is much less 

 prominent than the others. On the dorsal surface a pair of short longitudinal 

 serrate crests, some distance apart, connect the upper ends of the first and second 

 ridges, and form a strong tooth at the upper end of the first. The median keel 

 bears two procurved teeth, and a pair are set side by side on the ocular lobe. On 

 the lower part of the side of the carapace anteriorly a curved row of spines starting 

 from the pseudorostrum runs backwards and downwards towards the lower margin, 

 crossing the lower ends of the oblique ridges. The posterior edge of the carapace is 

 raised to form a marginal ridge which is strongest on the dorsal side. The ocular 

 lobe is twice as broad as long. There is no eye-pigment nor distinct corneal lenses. 



The posterior angles of the last thoracic somite are not produced. 



The abdomen is slender, about equal in length to the cephalothoracic region. The 

 somites have slight serrate dorso-lateral crests. The fifth somite is not greatly 

 elongated. 



Telson (figs. 89 and 90) a little shorter than the last somite, somewhat narrowed at 

 its base, its greatest breadth at about one-third of its length from the base, where it 

 bears a pair of lateral tubercles, then narrowing suddenly a little before the middle of 

 its length, the sides converging to an acute point. Viewed from the side (fig. 89), 

 the tip is seen to project beyond the obliquely placed anal valves by about one-third 

 of its length. A pair of very minute apical spinules are present, flanked by a pair of 

 small setae, with another pair of setae a little way further down the side. 



Antennules (figs. 78 and 78a) hardly reaching beyond the tip of the pseudorostrum, 

 the proximal segment more than twice, the third segment one and a half times the 

 length of the second. Outer flagellum shorter than the last segment of the peduncle, 

 consisting of three segments, the terminal one very minute. Inner flagellum two- 

 thirds the length of the outer, composed of two segments, the proximal very short. 



Antennas (fig. 80) consisting of three segments. 



Mouth-parts of normal type. Mandibles with about nine spines. Lobes of lower 



