LEPTOSTRACA. 457 



of the Malacostraca. Moreover, in the male, the vas deferens 

 opens at the base of the last thoracic appendages, and the oviduct, 

 in the female, apparently on the sixth. These characters 

 establish the fact that whatever affinities the Leptostraca 

 present to other groups, they are not far removed from the 

 Eumalacostraca. 



On the other hand the body is laterally compressed and covered 

 in front by a large bilobed transparent shield, a reduplicature of 

 the integument of the head. The two halves of the shield are 

 connected with one another by a shell muscle, as in the Cirripedes, 

 Ostracods and bivalved Branchiopods. A pointed head plate 

 projects in front of the shield, and presents the unusual feature 

 of being movably articulated with it (Fig. 284, E), a character 

 found in palaeozoic Ceratiocaridae, and appearing in a somewhat 

 different form in the Stomatopods. The abdomen is formed 

 of eight segments, including the telson, and is further peculiar 

 in being more or less distinctly differentiated into two regions 

 by the character of its appendages. 



The shallow- water forms of the Leptostraca have large stalked 

 eyes (though they are apparently blind inNebaliella (q. v.) ), but 

 a median eye is not found. The anterior antennae consist of a 

 four-jointed basal region, of which the fourth segment carries an 

 oval setose plate as well as an articulated flagellum. The 

 posterior antennae have three large basal joints and terminate 

 in an articulated flagellum which in the fully grown male is as 

 long as the body and beset with sensory hairs. The cutting 

 mandibles bear long 3- jointed uniramous palps. The first 

 maxillae bear two setose plates directed inwards and a long 

 slender dorsally directed terminal flagellum. The second 

 maxilla bears three inwardly directed setose lobes on its inner 

 margin and ends in two short rami. 



The fusion between the anterior thoracic segments and the 

 head, which occurs to a greater or less extent in nearly all the 

 Malacostraca, is not found in the Leptostraca. The eight 

 short thoracic segments bear eight pairs of uniform appendages 

 which present a remarkable resemblance to those of Phyllopods 

 (Fig. 285). An obscurely two-jointed basal portion, bearing 

 on its outer surface a two-lobed branchial epipodite (absent in 

 Nebaliella) terminates in a jointed and setose endopodite, and in 



