Mr. Westvvood on Arcturus, 69 



utrinque productis ; antic^ posticfeque constrictus, depressu?, 

 marginibus medioque dorsi duplici serie noduloso. Elytra spi- 

 nis horrentia. Femora inermia, tibiis unicalcaratis. 

 In honorem celeberrimi Schonherri denominatus. 



PLATE VIII. 



Fig. 2. The insect of the natural size. 2 a. The head seen in profile. 



2 b. The tarsus. 



XVI. Observations on the oscidant Crustaceoxs Genus 

 Arcturus of Latreille ; until the Description of a British 

 Species. Bi/ J. O. Westwood, F.L.S. S)C. 



[Read March 3, 1834.] 



Taking advantage of the presence of those distinguished men who 

 this evening honour us with their presence*, I beg leave to offer 

 to the notice of the Society the description of a curious genus of 

 Crustaceous animals, interesting not only on account of its com- 

 prising a species which has hitherto been found only in the Arctic 

 Seas, but also from the peculiar situation which its singular structure 

 entitles it to hold in the class of animals to which it belongs. 



The great division named by Dr. Leach Malacostraca Edrio- 

 phthalma, comprises those hard-shelled Crustacea which have three 

 pairs of foot-jaws, five pairs of legs, and two other pairs of organs 

 resembling legs, but which in the Lobsters and Crabs are converted 

 into additional foot-jaws ; they have also the thoracic portion of the 

 body divided into segments, and their eyes are not placed at the ex- 

 tremity of footstalks. 



This division comprises three orders : 1st, the Amphipoda, or Leap- 

 ing Shrimps, having the fore-legs generally large and cheliferous, and 

 the body compressed and narrow ; 2nd, the Isopoda, having the legs 

 of equal size and unarmed, with the body oval and depressed, and 

 composed of equal segments, — containing the Wood-lice and allied 

 groups ; and 3rd, the Lamodipoda, a singular group, having the body 

 slender and cylindric, with unequal-sized legs, some being chelifer- 

 ous, and the segments unequal. 



The genus Arcturus of Latreille, although agreeing in many of its 



* Captains Sir John and James Ross were present at the Meeting when this 

 memoir was read. 



ti -2 



