EURYCERCUS. 123 



a species of fresh-water Nais, which he calls the Lurco. 

 "So great is the voracity," he says,* "of this creature, that 

 I have seen a middle-sized one devour seven Lyncei in 

 half an hour. Five of these were moving about in the 

 first cavity, at the end of that time the other two, having 

 passed into the second, had become exhausted. "f 



This family contains seven British genera. 



1. EuRYCERCUS. — Subquadrangular ; abdomen very 

 broad, in form of a flat plate, densely serrated. 



2. Chydorus.— Nearly spherical in shape ; beak very 

 long and sharp, cm^ved almost into the shape of a crescent; 

 inferior antennae very short. 



3. Camptocerus. — Ovoid- shaped ; abdomen long, 

 slender, and extremely flexible ; serrated. 



4. Acroperus. — Shell somewhat harp-shaped, termi- 

 nating inferiorly on the anterior margin in a more or less 

 blunt point projecting forwards ; inferior antennse rather 

 long. 



5. Alona. — Shell quadrangular^ striated or grooved 

 longitudinally ; inferior antennae short. 



G. Pleuroxus. — Anterior margin prominent on the 

 upper portion ; the lower part being truncated, or, as it 

 were, cut sharp and straight ; first pair of feet very large. 



7. Peracantha. — Oval-shaped ; lower extremity of 

 shell slightly curved backwards, and, as well as upper 

 extremity of the anterior margin, beset with strong, 

 hooked spines. 



Geims 1 — Eurycercus.J 



Lynceijs, Midler, et cmdonm. 



EuKYCEKCUS, Baird, Ann. Mag. Nat. Hist, ii ; Trans. Berw. Nat. Club, ii. 



Character. — Subquadrangular. Abdomen very broad, 

 in form of a flat plate, densely serrated. Beak blunt, 

 slightly curved downwards. 



* Pritcliard's Micros. Cab , p. 81. 



f Vide supra^ p. 9. 



X From tvpvg, broad; and KtpKoi;, a tail. 



