634 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Family LAPHYSTIOPSID^. 



Mr. Shoemaker's account of the new amphipod found on Iridometra iiiel.po- 

 mene follows: 



LAPHYSTIOPSIS IRIDOMETR-E SHOEMAKER. 



Description of the male. — The eyes are without pigment, but clusters of indis- 

 tinct visual elements are present under the surface of the convex sides of the head. 



The head is broad and flat and produced in front into a horizontal, spatulate, 

 truncated lamella. 



The antennse are proportionately shorter than in L. planifrons Sars. The first 

 and second antennse do not differ greatly in length; the first has a flagelhun of 

 about 12 segments, the second a flagellum of about 10 segments. The first segment 

 of the flagellum of the first antennse is the longest and is provided with three 

 fascicles of sensory bristles. 



The perseon segments are separated from one another by slight transverse 

 depressions. The pleon segments are much deeper than those of the perseon, and 

 the first three are produced posteriorly into a blunt dorsal lobe; the fourth bears a 

 deep saddle-shaped depression. 



The mouth parts resemble in all essentials those of L. planifrons, but the first 

 segment of the mandibular palp is proportionately longer. 



The first four coxal plates are produced anteriorly, and the fifth and sixth are 

 more deeply bilobed than in L. planifrons. 



The gnathopods and pereeopods are all much more robust than those of L. 

 planifrons., and the last three are relatively shorter; the third, fourth, and fifth 

 consecutively increase but little in length. The first and second gnathopods are 

 similar in structure, the second slightly the larger. The fourth and fifth segments 

 of the gnathopods are triangular, the sixth is slightly longer than the fifth, and 

 both fifth and sixth are provided on their lower surface with fine setse and at their 

 distal ends with several longer setse. The dactyl is strong, well curved, and nearly 

 as long as as the sixth segment; the concave surface is provided with a row of fine 

 setas, and there are several longer ones near the point. 



The first and second perseopods are similar in structure, the second being 

 slightly the larger. The second segments are expanded anteriorly into a broad 

 lobe with evenly curved edges; tlie third segments are short; the fourth and fifth 

 are produced anteriorly into a broad lobe, directed slightly downward; the sixth 

 increases very suddenly in width, after which the proximal and distal edges are 

 nearly parallel. The dactyl is strong and well curved, about two-thirds as long as 

 the sixth segment. The third, fourth, and fifth perseopods are very much alike in 

 structure ; the coxal plate of the third is deeply bilobed : that of the fourth has the 

 anterior lobe deeper than the posterior; and that of the fifth is truncated anteriorly 

 and slightly lobed posteriorly ; the second segments of these three perseopods are ex- 

 panded posteriorly into a broad flat lobe of progressively increasing size, each more 

 expanded and more depressed than the preceding; the third segments are short; 

 the fourth are produced posteriorly into depressed lobes, each longer than the one 

 preceding; the fifth segments are short, and each is produced posteriorly into a 



