v FAMILIES OF CUMACEA 121 



epipodite and a large gill upon the basal joints. Pleopods are 

 only developed in the male sex. 



The flagellum of the second antennae in the male may he 

 enormously elongated, as in the Atlantic deep-sea species shown 

 in Fig. 80, so as to exceed in length the rest of the body. 



Fam. 1. Cumidae. Xo sharp demarcation between thorax 

 and abdomen. Four posterior pairs of legs in both sexes with- 

 out exopodites. Male with five well-developed pleopods in addi- 

 tion to the uropods. Telson wanting. Cv.ma, Cyclaspis, etc. 



Fam. 2. Lampropidae. Body -form resembles that of 

 Cumidae. All the thoracic limbs except the last have exopodites. 

 The male has three pairs of pleopods. Telson present. Lamprops, 

 Platyaspis, etc. 



Fam. 3. Leuconidae. Body-form similar to above. Male 

 has only two pairs of pleopods. Mouth-parts peculiar, much less 

 setose than in other families. Telson absent. Leucon, Eudorella. 

 Fam. 4. Diastylidae. Anterior part of thorax sharply 

 marked off from posterior part. Male has two pairs of pleopods. 

 Telson present. Diastylis (Fig. 80). D. goodsiri from the Arctic 

 ocean measures over an inch in length. 



Fam. 5. Pseudocumidae. Bather similar to Diastylidae, 

 but differ in reduced size of telson and presence of exopodites 

 on third and fourth thoracic legs of female. This family is 

 represented by three very similar marine forms of the genus 

 Pseiidocuma ; but, as Sars has shown, 1 the Caspian Sea contains 

 thirteen peculiar species, only one of which can be referred to the 

 genus Pseudocuma, while the rest may be partitioned among four 

 genera, Pterocuma, Stenocuma, Caspiocuma, SckizorJiyncJws. 



Order III. Isopoda. 



The Isopoda and the Amphipoda are frequently classed together 

 as Arthrostraca or Edriophthalmata, owing to a number of features 

 which they share in common, as, for instance, the sessile eyes 

 which distinguish them from the podophthalmatous Schizopoda 

 and Deeapoda, the absence of a carapace, and the thoracic limbs 

 which are uniramous throughout their whole existence. For the 

 rest, in the presence of brood-plates and the other diagnostic 



1 Sars, "Crustacea Caspia," Bull. Acacl. Imp. Sci. St. Pttersbourg, series 4, 

 xxxvi., 1894, and "Crustacea of Norway," iii., 1900, ]>. 120. 



