ISOPODA OE THE 'LIGHTNING' AND OTHEE EXPEDITIONS. 113 



last three pairs of legs {i.prp i t l.jarp 4 *) the finger in like manner issues from a crowd 

 of finely serrated spines, but it greatly exceeds them all in length, and is itself orna- 

 mented with a set of spines round its distal end, which shade off into lines of finer and 

 finer spinelets running backwards towards its base ; from the midst of the distal circlet 

 of spines springs a long wavy spine-nail. 



The first four free perseon-segments carry the small plates which are destined to be 

 developed into the incubatory pouch. 



The first five segments of the pleon bear each a pair of pleopods, consisting of a 

 peduncle and two much ciliated branches, of which the inner has one pair of setae 

 springing from a prominent angle not far from the base of the plate (i. pip and 

 i. pip*). 



The uropods (i. t) spring from the widest portion of the last caudal segment, the 

 peduncle not reaching beyond the termination of the segment ; the inner ramus con- 

 sists of nine articulations, and is about as long as the antennae ; the outer ramus is 

 minute, and composed of two articulations, which are together not so long as the 

 first of the inner filament. This latter has the alternate joints slightly ciliated. 



Length of a large specimen 8 - 5 millim., or about one third of an inch. 



This species was procured in the ' Porcupine ' Expedition of 1869, Station 19, lat. 54 a 

 53' N., long. 10° 56' W., 1360 fathoms, and Station 30, lat. 56° 24' N., long. 11° 49' W., 

 1380 fathoms ; and, subsequently, by the 'Valorous,' Station 15, in lat. 56°11'N., long. 

 37° 41' W., at a depth of 1450 fathoms, on a bottom of globigerine mud and pebbles. 



2. Alaotanais hastigee, n. sp. (Plate XXIII. fig. n.) 



This species comes very near to the last. It differs from it in having the eye- 

 processes relatively larger, and in the massiveness of the hand and finger of the first 

 gnathopods (n. gn 1 ) ; in these organs all the parts are thickened and strengthened, 

 without any proportionate increase in length. The effect of this is to make the inner 

 edge of the thumb and finger overlap when closed all along the line, except for a small 

 triangular space near the root of the thumb. 



The uropods have the inner branch nine-, the outer two-jointed. 



But the characters which at once distinguish this species from all others known to 

 us are to be found in the microscopic armature of the limbs. All the perBeopods are 

 everywhere beset with long, very slender spines, the whole of which, under high 

 powers, are found to be covered with minute prickles. There are no toothed spines, 

 such as are found in Alaotanais serratispinosus (PI. XXIII. fig. 1, gn 2 ), the cor- 

 responding limb to which in A. hastiger has the finger long, narrow, and curved, and 

 surrounded by a series of long, very slender spines, which all have the character of 

 being beset irregularly all round with little prickles. 



The hinder perseopods (ii.ptp 5 ) have a finger which, so far as we are aware, is abso- 

 lutely unique in structure : the propodos is cleft at the end to some depth, the cleft 



