REPORT ON THE AMPHIPODA. 1025 



observation does not entirely confirm Mr. Chilton's, for in the Challenger specimens they 

 appear to run out as usual to a fine apex, unless where broken or surmounted by some 

 parasitic growth, although it is quite true that for almost the whole length the thickness 

 is uniform. 



Elasmopus delaplata, n. sp. (PI. XCIX.). 



Rostrum rudimentary, lateral lobes of the head with flattened curve, and a small lobe 

 just below and a little to the rear ; first and second segments of the pleon with the 

 posterolateral angles not very sharp, the third segment with these angles rather out- 

 drawn, the lower part of the hind margin rather strongly serrate, and one serration on 

 the lower margin just behind the angle ; submarginal spines on all the three segments. 



Eyes rather small, oval, placed near the margin of the lateral lobes, white in the 

 specimen preserved in spirits, the ocelli small. 



Upper Antenna; with the peduncles and flagella respectively much longer than those 

 of the lower pair ; first joint elongate, narrowing a little distally, longer and thicker than 

 the second joint, carrying a few cilia ; second joint widening a little distally, carrying 

 several groups of setae on either side; third joint shorter than the second, but also' 

 elongate, widening distally, and carrying many groups of setae ; the flagellum longer than 

 the peduncle, of thirty-five joints, the last minute, tipped with setae, the others carrying 

 two apical groups of setae and a cylinder ; the secondary flagellum slender, consisting of 

 three long and one short joint, the tip of which reaches the end of the fourth joint of the 

 primary flagellum. 



Lower Antennae. — First three joints very short, lobe of the first not protruding, 

 gland-cone decurrent, reaching the end of the third joint, fourth joint much longer than the 

 first three united, nearly as long as the second of the upper antennae, carrying several 

 groups of setas ; fifth joint a little shorter, much more slender, carrying many groups of 

 setae; flagellum of sixteen joints, the first as long as the two following together, the 

 others increasing in length from the second to the thirteenth, all carrying apical groups 

 of setae, and, all but the last three, central groups also. 



Upper Lip tending to circular, with the distal margin a little flattened, ciliation slight. 



Mandibles. — Cutting plate with an almost smooth edge, bounded by a not very 

 prominent tooth at the top, and two large ones below; secondary plate of the left 

 mandible, broad at the base and the distal margin, the latter cut into five strong teeth, of 

 which the lowest is the largest ; in the Plate these teeth are seen in profile ; on the 

 right mandible the secondary plate is bifid, the forward tooth the longer, both more or 

 less denticulate; the spine-row on the left mandible of four, on the right of three, 

 denticulate curved spines ; the molar tubercle massive, dilated at the crown, which is 

 surrounded by denticles, covered on one side by a honeycomb pattern, and carries 



(ZOOL. CHALL. EXP. — PART LXVII. — 1887.) XxX 129 



