ACROPERUS. 129 



short, from last ; posterior branch has only three long 

 filaments and one short, from the last joint. 



Abdomen (t. XVI, f. 9 a) very long and slender, with 

 thirteen well-marked serrse, or teeth, on lower edge, and 

 several smaller ones, terminating in two long and slender 

 claws ; setae short. This organ, and lower part of body, 

 is extremely flexible, and the animal can twist it com- 

 pletely ronnd in a circle, and then unbending it, thrust 

 it far out beyond the shell. 



First pair of feet large. 



Intestine convoluted, having one complete convolution, 

 and half another. 



Hab. — Ditch near Richmond. Pond near Smallborough 

 Green, Hounslow. Highgate ponds. June, Jidy, and 

 August. 



Genus 4 — Acroperus.* 



Lynceus, Baird, Traus. Berw. Nat. Club, i. 



AcKOPERUS, Baird, Aim. and Mag. Nat. Hist., ii ; Trans. Berw. Nat. 

 Club, ii. 



Character. — Shell somewhat harp-shaped, terminating 

 inferiorly on anterior margin, in a more or less blunt 

 point, projecting forwards. Inferior antennae, or rami, 

 long. Beak blunt, curved downwards. 



I. Acroperus harp^. Tab. XVI, fig. 5. 



Lynceus HARP^, 5««W, Trans. Berw. Nat. Club, i, 100, t. 2, f. 17, 1835. 

 Acroperus harp^, Baird, Ann. and Mag. Nat. Hist., ii, 91, t. 3, f. 7, 



1843 ; Trans. Berw. Nat. Club, ii, 151. 

 Lynceus leucocephalus, Zbc//, Deutsch. Crust., h.xxxvi, 1. 10,1841. 



Shell rounded posteriorly, sinuated rather deeply, and 

 ciUated anteriorly ; terminating in an obtuse point, pro- 

 jecting forwards; strongly striated, or rather ribbed, 

 longitudinally and somewhat obliquely, giving the shell, 



* From n/cpoc, pointed ; and tt? ^ac, extremity. 



9 



