yn.v.m. DESCniPTlnXS OF AEGULID.IJ—WILSOX. (J45 



the}' have not been sought in a single locality without success. When 

 kept in aquaria they are lively, moving about and changing from one 

 tish to another more often than other spocios. Tlie long plumose setie 

 upon the swimming legs make powerful oars atid enable them to dart 

 al)Out with great rapidity. One of their favorite movements is to 

 leave the side of the aquarium and, turning back downward, scuttle 

 swiftly along the under side of the surface ti.lm of the water after the 

 manner of the very much slower aquatic snails. 



(rENKRAL FORM — DorHttlHurface (fig. 22). — Carapace almost perfectly 

 orbicular, the antero-lateral sinuses shallow, but leaving a well-rounded 

 frontal lobe; the posterior sinus is one-third the length of the cara- 

 pace and only one-sixth its width, so that the lateral lobes are broad 



Fig. 22. — DoRs.\r. vikw of fkm.\i.k. .\RGrLi\s versicolok. 



and well rounded. In the female they just reach the alxlomen; in the 

 male they overlap it somewhat. The free thoracic segments are 

 twice as wide as long and are half concealed beneath the carapace 

 lobes on either side. The abdomen has a very graceful oval out- 

 line in the female and is about three-sevenths the length of the 

 carapace. In the male it is more nearly triangular, but narrows 

 considerably anterior to the testes, and the lateral margins project 

 forward in a well-detined and rounded lobe on either side. The anal 

 sinus is very short and slit-like, with the papilhv subterminal.^ 



The arrangement of the grooves dividing the carapace into its areas 

 is very symmetrical. The longitudinal ri])s are close together, and 

 the joints in them just behind the brain can be clearly seen. The 



