20 CRUSTACEA—BRANCHIOPODA CHAP. 
side being nearly flat, the dorsal surface convex; the hinder 
margin of the head is indicated dorsally by a transverse cervical 
ridge, bounded by two grooves, behind which the carapace projects 
backwards as a great shield, covering at least half the body, but 
attached only to the back of the head. In Lepidurus productus 
the head and carapace together form an oval expansion, 
deeply emarginate at the hinder, narrower end, the sides of 
the emargination being toothed. The carapace has a strong 
median keel. The kidneys project into the space between the 
folds of skin which form the carapace, and their coils can be 
seen on each side, the terminal part of each kidney-tube enter- 
ing the head to open at the base of the second maxilla. In all 
Jal 
Fia. 2.—Chirocephalus diaphanus, female, x 5, Sussex. D.O, Dorsal organ; H, heart ; 
Ov, ovary; U, uterus; V, external generative opening. 
Branchiopoda with a well-developed carapace the kidney is enclosed 
in it in this way, whence the older anatomists speak of it as the 
“ shell-gland.” 
Associated with the development of the carapace, in this and 
in the next family, is a remarkable condition of the lateral eyes, 
which are sessile on the dorsal surface of the head, and near the 
middle line, the median eye being slightly in front of them. 
During embryonic life a fold of skin grows over all three eyes, so 
that a chamber is formed over them, which communicates with 
the exterior by a small pore in front. 
In the LirwnapiparE the body is laterally compressed, and 
the carapace is so large that at least the post-cephalic part 
of the body, and generally the head also, can be enclosed 
within it. 
In Limnetis (Fig. 3) the dorsal surface of the head is bent 
downwards and is much compressed, the carapace being attached 
