ALTEUTHA. 
217 
setae. From the opaqueness of the body, and the flatness 
of its form, I could not distinctly perceive the mandibles 
or foot-jaws ; except that the latter were like the corre- 
sponding organs in the Canthocamptus. The first pair of 
feet (t. XXX, f. 1 a) is composed of two stalks rising from 
one common base, each stalk consisting of three joints. 
The superior or external stalk is longer than the inferior, 
the last joint terminating in four short hooks. The in- 
ferior stalk terminates in several short setae, and has a long 
filament at each joint. The other legs are of the same 
form and structure as in the preceding genera, and pro- 
vided with numerous long hairs. 
At the junction of the first with the second segment of 
the abdomen, there issues on each side an organ (f. \b), very 
much resembling the fulcra or supports we find occurring 
at the same part of the body in the other genera already 
described, only that in this little creature we observe the 
same sort of organ in the male as well as in the female. 
It consists of a broad, falciform plate, which terminates in 
a tolerably long, bluntish, hollow spine, having four short 
teeth or hollow spines (in the male) on the outer edge, 
the whole organ being nearly equal in length to the 
abdomen. In the female these organs are not quite so 
large as in the male, and have only two short teeth on the 
outer edge, both of which are situated near the base. In 
the female also, the second segment of the abdomen is 
much larger than in the male. The posterior two thirds 
of the thoracic segment is marked with a broad fascia of 
a very dark colour, with a ruby tinge in it. The two 
upper segments of the abdomen are marked in the same 
manner, but not of so deep a hue. 
The ovary is single, large, round, lying right across the 
abdomen. 
The motion of this little creature is very peculiar. It 
generally swims on its back, and instead of darting/br- 
ward through the water, as the other species of this family 
do, it springs with a bound from the bottom of the vessel, 
where it rests when undisturbed, up to the surface of the 
