84 



ARTIIROPODA. 



are somewhat different in form and with fewer limbs: in Arctu- 

 ridse they are carried for some time clinging on to the antennas 

 of the mother. In ordinary Isopoda they are retained for a time 

 in a kind af pouch formed by the membranous plates at the base 

 of the legs. The sexes are often more or less dissimilar. 



In the terrestrial Oniscidse the two or four anterior pairs of 

 branchiae are modified into lungs or air-vessels. 



Some of the Oniscidse are land animals, and are known as 

 hog-lice, sows, &c. One of our English species, Platyarthrus 

 Hoff/nanseggii, is found in ants' nests. Limnoria terebrans is very 

 destructive to submerged timber. JEga spongiophila resides in 

 Euplectella aspergillum. Bopyrtis squitlarum is found commonly 

 under the skin of prawns. Liriope is a parasite on Peltogaster, 

 itself a parasite. 



Limnoria (Gribble). 



laera. 



Munna. 



Ceratothoa. 

 Eurydice = Slab- 



berina. 

 Cirolana. 

 ^Ega. 

 Serolis. 



Munnopsidcs. 

 Munnopsis. 



Asellidce. 

 Asellus. 



Bopyrus. 



lone. 



Liriope. 



Gyge. 



Phryxus. 



Oniscid(B. 

 Ligia. 

 Oniscus. 

 Porcellio. 

 Platyarthrus. 

 Philoscia. 

 Armadillo. 

 Tvlos. 



Subclass Y. PODOPHTHALMA. 



THORACOSTRACA. 



Eyes on movable peduncles. Head and thorax confluent, 

 covered by a shell or carapace. 



The masticatory parts of the mouth [gnathites] are very com- 

 plicated, the two or three anterior pairs of thoracic limbs being 

 converted into foot-jaws [maxillipeds or pedipalpsj, and subject 



