KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 52. N:0 |5. 5 
1910 in >billabong», clay-pans with muddy water, in this case rather deep and 
very likely filled with water all the year round. 
Description of the female. 
Dorsal margin of shell marked off from the anterior margin by a distinct 
angle, and from the posterior margin by a prominent spine, into which the latter 
is continued. Dorsal margin from anterior angle to umbo straight, sloping upwards 
and backwards; from the umbo it rises more or less abruptly, then falling gradually 
towards the posterior and usually rising slightly near its termination. A varying 
number (one to twelve according to SPENCER and HALL, here on this single specimen 
six spines) of backwardly directed serrations correspond to the intervals between the 
lines of growth. Anterior, inferior and posterior margins forming together a fairly 
regular ellipsoidal curve. Lines of growth eleven clearly-marked, thread-like elevated 
ridges on the single specimen present. Dimensions of shell: length 24 mm, height 17 mm 
Fig. 1. Shell of the female specimen viewed from left side; 
magnified about 17/7 times. 
and thickness through both valves 4,6 mm. The whole body of the animal is con- 
tained within the shell to which the animal is attached in the region of the umbones 
and by the adductor muscles. 
The uniting organ is situated somewhat behind the eye in the upper edge 
of the head and is pear-shaped, being attached by its smaller end. Lower edge of 
the antennule straight, upper edge pectinate, with sixteen small, blunt, rounded 
projections. The proximal undivided part of the second antennae is pectinated on 
its upper edge, the projections being about ten in number and corresponding to 
transverse lines on the inner face of the basal portion. A few plumose setae rise 
from the denticles. The distal part of the second antennae consists of two rami, the 
upper being slightly shorter than the the lower one. Each joint bears on its upper 
surface a number of short stout setae, and on its under surface a larger number of 
long plumose setae. 
Feet about thirty pairs in number as in the male, increasing in size from the 
fore part backwards as far as to about the fifth pair. At about the fifteenth pair 
they begin to decrease gradually, and are extremely small at the posterior end of 
the body. 
The spinous plate processes of the dorsal egde of the telson each bear very 
many denticles, which increase in length posteriorly to the terminal spine. The 
