Descriptions of some Australian Phyllopoda. 19 



The valves ai^e perfectly equal, and connected along the 

 greater part of their dorsal side, without any intervening true 

 hinge. When the shell is closed, and the animal completely 

 withdrawn into its cavity, the free edges of the valves fit 

 closely together everywhere. More frequently, however, they 

 are found to be slightly apart, permitting some of the ap- 

 pendages of the animal, especially the rami of the antennæ, 

 to be stretched out from the shell. Sometimes even the frontal 

 part of the head and the tail is seen partly projecting beyond 

 the edges of the valves. 



As to consistency, the valves are rather thin and flexible, 

 chitinous in character, and without any calcareous deposit. They 

 exhibit on the outer face numerous lines of growth, running 

 parallel to each other and to the free edges, only wanting on 

 the umbonal part of the shell. Their number may increase to 

 20 or 30 in all, some of them being very conspicuous, whereas 

 others are only faintly traced. The surface of the shell is 

 otherwise quite smooth and polished, without any conspicuous 

 sculpturing, and also wanting any trace of hairs or spines. 



Between the 2 lamellæ of each valve is imbedded the 

 shell-gland, which takes its origin from the place, where the 

 adductor muscle of the shell joins the inner face of the valve. 

 This gland is only faintly traced externally, but is found, on 

 a closer examination, to exhibit much the same structure as 

 in Limnadia. 



In younger, yet sexually developed specimens (figs. 3 & 4) 

 the shell exhibits a form rather different from tliat in fully 

 grown females, the umbones being far less prominent, and the 

 valves accordingly more regularly oval or elliptical in shape, 

 with a much smaller number of lines of growth. 



In still younger specimens the umbones are not at all 

 distinguishable, the dorsal margin being quite evenly arcuate, and 

 the lines of growth are reduced to from 3 to 5 only in number. 



