28 CEYLON PEARL OYSTER REPORT. 



and somewhat upwards." In Cterissa pterygoid (Koelbel) there is a similar 

 expansion of the side plates, hut it applies to all six of them on one side of the 

 animal and to none on the other side. 



Irona nanoides, n. sp. Plate VI. (B). 



The specimen, a female, having its pouch enormously distended with young ones, 

 was slightly distorted so as to make the outline of the left side very convex. The 

 middle of the back is raised considerably above the lateral parts of the segments. 

 The head has a short, very broad front. The peraeon is very broad, the side-plates of 

 the fifth segment approaching the character of the two following pairs. The first two 

 segments of the pleon are overlapped by the last segment of the peraeon, the next 

 three are very short but wider than the almost semicircular telsonic segment. 



The eyes are wide apart, not very large, black. The first antennae are rather stout, 

 especially as to the first three of the eight joints. The ten-jointed second pair are 

 slighter, subequal in length. The upper lip has a four-lobed margin as in Ar&locra 

 cuvieri, Leach, and in Renocila periophthalmi, Stebbing. The mandibles have a 

 stout first joint to the palp, the second much thinner and a little shorter, the third 

 shorter and thinner than the second, and armed with a few spines. The trunk thins 

 out in advance of the palp, apparently carrying a quasi-molar not very remote from 

 the pointed cutting-plate. The slender first maxilla is tipped with five spinules. 

 The second maxilla appears to have a membranous apical margin accompanied by a 

 process carrying small hooked spines. The maxillipeds have the composite second 

 and third joints long and broad, followed by a joint which is about equal in length 

 and breadth, narrowed at the rounded apex, to which is attached the narrow terminal 

 bearing two outward bent hooks at its summit and one such hook on its side. 



The gnathopods and perteopods are all very similar in appearance and structure, 

 the hinder pairs having some superiority of size. The second joint is substantial, but 

 not conspicuously expanded ; the third in the gnathopods is as long as the hand, but 

 in the hinder peraeopod is longer than any one of the joints that follow it ; the fourth 

 joint is short but wide, being especially bulging in the fifth peraeopod ; the fifth joint 

 is of insignificant size, tending slightly to underride the short curved hand, which 

 does not exceed in length the simple but strongly hooked finger. 



The pleopods are all of remarkable breadth, both branches similar in structure and 

 devoid of setae. The coupling spines of the short peduncles are small. The uropods 

 are short, with two subequal oval branches, little longer than the stout peduncle, of 

 which the inner apex is not produced. There are some tiny spinules on the branches, 

 of which the inner is decidedly not longer than the outer. Colour in spirit yellow, 

 with the upturned side-plates whitish. 



Length 10 millims., greatest breadth 5 "5 millims. 



Locality: Station XXXIX., Gallehogalle Bank, 16 to 20 fathoms. 



The young ones taken from the mother's pouch have the broad front to the head as 



