PLEUROXUS. 279 



Hab. Ponds and ditches in Scotland and England. 



Acroperus nanus, Baird. — Not a seventh part the size 

 of the preceding. 



Hab. Pond at Norwood Green, and near Southall, Mid- 

 dlesex. 



Gen. 152. ALONA, Baird. 



Shell quadrangular, striated longitudinally. Lower an- 

 tennae short. Beak blunt and nearly erect. 



Alona quadrangularis, Muller, sp. — Shell transparent, 

 deep-brown. 



Hab. Ponds and ditches. 



Alona reticulata, Baird. — A very small species, with a 

 closely reticulated shell. Pound by Dr. Baird in a pond near 

 Southall. 



Alona ovata, Baird. — Ovate, transparent, larger than A. 

 quadrangularis. 



Hab. Pond on Blackheath. 



Gen. 153. PLEUKOXUS, Baird* 

 Pront margin prominent on upper part ; lower part trun- 



* TI\evpov, a side, and o£vs } sharp. 



