CHI ROCEPH ALUS. 
263 
place near London where he has met with it, is on Black- 
heath. “They swim upon their back, and in fine warm 
weather, when the sun is not too strong, they may be seen 
balancing themselves, as it were, near the surface by means 
of their branchial feet, which are in constant motion. On 
the least disturbance, however, they strike the water rapidly 
with their tail from right to left, and dart away like a fish, 
and hasten to conceal themselves by diving into the soft 
mud, or amongst the weeds at the bottom of the pool. 
It is certainly the most beautiful and elegant of all the 
Entomostraca . The male is especially beautiful. The un- 
interrupted undulatory wavy motion of its graceful bran- 
chial feet, slightly tinged as they are with a light reddish 
hue, the brilliant mixture of transparent bluish-green and 
bright red of its prehensile antennae, and its bright red tail, 
with the beautifully plumose setae springing from it, render 
it really exceedingly attractive to the view. The undulatory 
motion of its branchial feet serves another purpose in addi- 
tion to that of keeping the animal suspended in the water. 
The thorax or body of the animal has been described, when 
floating on its back, as like the cavity of a little boat, the 
feet representing the oars. When these are in motion, they 
cause the water contained in this cavity to be compressed, 
