DESCRIPTION OF A NEW SPECIES OF GAMMARUS. 545 



palm slightly oblique, palmar margin crenulate and beset with small 

 sensory spines, palmar angle with one long and two short spines on 

 the outer side, and one long and one short on the inner. In Gnath. 2 

 the fifth and sixth joints are equal in length and of equal width 

 throughout, both provided posteriorly with clusters of straight setae, 

 palm transverse, with the margin rounded, and spines as in Gnath. 1. 



Feraeojjod lin the male has the posterior margins of the fourth, fifth, 

 and sixth joints beset with clusters of the sensory coiled hairs. 



Femeopod 3 elongate, the hind expansion of the basal joint lightly 

 crenulate, hind lobe free. Peraeopods 4 and 5 not much longer than 

 pp. 3 ; the basal joint expanded above, gradually narrowing to the 

 distal angle, where one or two strong spines are inset. In the female 

 these joints, especially that of the fifth, differ in shape from those of 

 the male ; they are expanded above, but about two-thirds down they 

 suddenly narrow ; several long plumose hairs are inset on the inner 



Fig. 5. — Gnathopod 2. S Ganimarus chevreuxi, n. s\i. Outer side, x 27. 



side. All the hinder peraeopods are furnished with spines, most 

 numerous on the fifth. 



The incubatory lamellae occur on segments 2 to 5. 



The branchial vesicles are on segments 2 to 7 ; they are borne on 

 stalks, are ovate in form, and densely fringed with tangled hairs round 

 the tip and along the posterior margin, especially in the male. 



Urojjods. The first pair extend beyond the second. In the third 

 the inner ramus is not much more than a half the length of the outer, 

 both thickly beset in the male with tufts of the characteristic sensory 

 hairs, intermixed with long straight setae. This pair of uropods is 

 shorter in the female, and is furnished with long spines and straight 

 and feathered setae. 



The tclsoii has an apical group of three spines ; of the two lateral 

 groups the upper one carries two spines and one or two setae, and the 

 other one spine and one or two setae. 



