SESSILE-EYED SERIES 



3243 



the former distinguishable from the latter by its duller color and the granules upon 

 its segment; Oniscus being smooth and more or less variegated. Both these are 

 rather flat, and incapa- 

 ble of rolling up into a 

 ball; but the pill wood 

 louse ( A rmadillidium 

 vulgare} has the dorsal 

 surface more convex, 

 and when handled rolls 

 up into a ball. On ac- 

 count of their resem- 

 blance to pills, these 

 creatures were used for 

 various maladies. In 



addition to its rounder FRESH-WATER SHRIMP (enlarged), 



shape, the pill wood 



louse may be recognized by the fact that the appendages of the last abdominal segment 



(the uropods) do not project like a couple of small tails 

 from the hinder end of the body. Members of this group, 

 differing but little from the species described, are widely 

 distributed in all temperate and tropical parts of the world. 

 The tribe Phreatoicidea can only be briefly noticed. 

 It contains the genus Phreatoicus, of which two species 

 both inhabiting fresh water are known, one from 

 New Zealand, and the other from Australia. The body 

 is long and laterally compressed, the seven thoracic ap- 

 pendages are well developed, and the first is subchelate 

 as in many Amphipoda, and the abdomen consists of six distinct segments, with the 

 gills attached to its appen- 

 dages. The last tribe, Chelif- 

 era, containing the genus Tan- 

 ais and others, approaches the 

 next order, and is distinguished 

 by having the first pair of ap- 

 pendages following the jaws 

 that is the second maxillipedes 

 pincer-like. It further dif- 

 fers in that the abdominal 

 limbs are used rather for swim- 

 ming than for respiration; the 

 breathing chamber is situated 



SAND HOPPER (enlarged). 



in the posterior 

 the thorax, and 



portion of 

 a constant 



SPINY SHRIMP, Acanthechinus tricarinatus (natural size). 



circulation of water is kept up within by the movement of a process projecting 

 backward from the maxillipedes. 



