ACROPERUS. 129 



short, from last; posterior branch has only three long 

 filaments and one short, from the last joint. 



Abdomen (t. XVI, f. 9 ) 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 round 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. 



Hob. Ditch near Richmond. Pond near Smallborough 

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

 August. 



Genus 4 ACROPERUS.* 



LYNCEUS, Saird, Trans. Berw. Nat. Club, i. 



ACUOPERUS, Saird, Ann. 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. 



1. ACROPERUS HARP^E. Tab. XVI, fig. 5. 



LYNCETTS HARPJE, Baird, Trans. Berw. Nat. Club, i, 100, t. 2, f. 17, 1835 . 

 ACROPERTJS HARP.E, Baird, Aim. and Mag. Nat. Hist., ii, 91, t. 3, f. 7, 



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

 LYNCEUS LEUCOCEPHALUS,.O<?//, Deutsch. Crust., h.xxxvi, 1. 10,1841. 



Shell rounded posteriorly, sinuated rather deeply, and 

 ciliated anteriorly ; terminating in an obtuse point, pro- 

 jecting forwards; strongly striated, or rather ribbed, 

 longitudinally and somewhat obliquely, giving the shell, 



* From nicpoc, pointed ; and ire pas, extremity. 



9 



