ALTEUTHA. 217 



setoe. Prom 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. 1(5), 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/or- 

 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, uj) to the mrface of the 



