GAMMARIDEA. 945 



The legs of the last three pairs have the claw turned outward ; the 

 setae are very slender and fully as long as half the fifth joint; and at 

 the apex of this joint there is a large cluster of them. The setae on the 

 upper apex of the joints of the superior flagellum are not longer than 

 the breadth of the joint; and below, on alternate joints, they have the 

 same length, while on the others they are twice as long. Both pairs 

 of antennae have a naked appearance. 



Genus GAMMARUS (Fabricius), Dana. 



Antennce superiores appendiculatce. Styli caudales postici ac in Iphi- 

 media, scepe longiores. Epimerce btce ^tis plus minusve breviores, bilo- 

 batce, lobis subcequis. 



Superior antennae appendiculate. Caudal stylets of last pair as in Iphi- 

 rnedia, often longer. Epimerals of fifth segment more or less shorter 

 than fourth, bilobate, lobes subequal. 



All the following species have the superior antennae the longer. The 

 branches of the posterior stylets are without spines, and furnished with 

 only a few hairs in all the species, excepting one from Puget's Sound ; 

 in this, one of the branches, the stouter one, bears spines, though still 

 different from the branches of the preceding pairs ; and the other or 

 thinner branch, has only short hairs. 



The true Gammari have generally smaller epimerals than the Amphi- 

 thoe, and differ from them widely in the non-uncinate posterior stylets, 

 and in the fifth epimerals not larger than the fourth, and subequally bi- 

 lobate. They approach most nearly to the Iphimedice, from which they 

 differ mainly in the absence of the appendage from the superior an- 

 tennae in the latter. If this appendage is not accepted as a generic 

 distinction, the groups may properly have a subgeneric relation. 

 Melita and Mcera also will have a like relation. 



1. Abdominis segmenta dor so plus minusve spinulosa aut denticulata. 



Gammarus aspek. 



Carpus crassiusculum, epirneris latis, btis vix brevioribus quam itce, seg~ 



237 



