176 CEYLON PEARL OYSTER REPORT. 



p. 685), from Japan, presents a great resemblance to this species in general form, in 

 the shape and proportions of the telson, and in the sculpturing of the carapace. Its 

 third maxilliped is not described, but it possesses rudimentary exopods on the third 

 and fourth legs, a character which led to its being referred to the genus Leptostylis, 

 although differing in several points from the typical members of that genus. Should 

 it prove to be the case that L. brevicaudata is without an exopod on the third 

 maxilliped, it will, I think, be necessary to include it with the present species in the 

 o-enus Paradiastylis in spite of the difference in structure of the third and fourth 

 legs. In the Diastylopsis dubia of Bonnier (' Ann. Univ. Lyon,' " Campagne du 

 ' Caudau,'" Edriophthalmes, p. 559), the jjresence or absence of rudimentary exopods 

 on these limbs seems to be a matter of individual variation, suggesting that no great 

 importance can attach to this feature as a generic distinction within the family 

 Diastylidse. 



Family : NANNASTACID^. 



Nannastacus stebbingi, n. sp. Plate V., figs. 91 to 93. 



Description of adult Male. Total length, L38 millims. : 



Carapace a little over one-third of total length, rather broader than deep, dorsal 

 surface a little depressed in middle line between the swollen branchial regions. On 

 either side, a little way behind the eye, is a rounded knob-like prominence (present 

 also, although less conspicuous, in N. unguiculatus). Pseudorostrum, seen from the 

 side, upturned and rounded, with two faintly marked ridges parallel to its distal 

 margin ; immediately below the pseudorostrum, and above the insertion of the 

 antennule, the concave antero-lateral margin bears a group of three curved spines, of 

 which the upper and largest is very conspicuous. Antero-lateral angle not produced, 

 rounded, not serrate, but with a single small spine springing from the outer surface. 

 Seen from above, the pseudorostral plates do not meet in front of the eyes and the 

 respiratory channel is widely open. The eyes are large, each with three prominent 

 corneal lenses. The width of the interocular margin is about equal to the diameter 



of the eye. 



All the free thoracic somites have sub-marginal lateral crests of laminar spines, the 

 last three also with paired serrated crests on the dorsal surface. 



Abdomen shorter than the cephalothoracic region, fifth somite not much longer 

 than the preceding. As in N. unguiculatus, all the somites bear serrated lateral 

 crests overhanging the lateral grooves, and each, except the last, has a pair of stouter 

 dorsal crests ending behind in a strong curved tooth. On the last somite, apparently, 

 the lateral crests alone are present running on to the dorsal surface, and the posterior 

 border of the somite is produced into a sharp median spine. 



In the last pair of legs the carpus is longer than the propodus. 



Uropods (fig. 93), excluding the apical spines, longer than the last two somites ; 



