303 



ZOOLOGY. 



Pig 



leg of male JCulim- 

 nadia com.plexima- 

 nus a, hand ; b, 

 end of body. 



This suborder presents a beautiful series of increasingly 

 complex forms, as we ascend from Limnetis to Branchipus. 

 In Limnetis the bivalve shell encloses the ani- 

 mal, and is the size of a small flattened pea. 

 There are from ten to twelve feet - bearing 

 segments. L. GoiihlU Baird (Fig. 243) is very 

 rare in Canada and New England. The shell 

 of Linmadia is thin, oval, and there are from 

 eighteen to twenty-six feet-bearing segments. 

 L. {Eulimnadia) Agassizii Packard (Figs. 344 

 and 245) inhabits pools in Southern New En- 

 gland. The shell of Estlieria (Fig. 246, Es- 

 theria Belfragei Packard) is sometimes mis- 

 taken for that of the fresh - Avater moUusks 

 Cyvlas and Pisiditmi. The males of the fore- 

 going genera have the first pair of feet modi- 

 fied to form large claspers (Fig. 24.5). 



In Apus the abdomen projects beyond the large carapace, 

 and ends in two long many-jointed appendages. There are 

 about sixty pairs of feet, each foot 

 divided into several leaf -like lobes, 

 wherein respiration is carried on. 



Tliese Pliyllopods usually swim upon 

 their backs, as in the species of Bran- 

 chipus. The females chiefly differ 

 from the males in the presence of an 

 orbicular egg-sac on the eleventh pair 

 of feet, the sac being a modification of 

 two of the lobes of the feet, and containing but a few eggs. 

 A^ms mqualis Packard (Fig. 347, Fig. 249 A, represents the 

 larva of a European Ajms) inhabits pools in the western 

 plains. Lepidunis differs from Apns in having the telson 

 spoon-shaped instead of square. L. C'ouesii Packard (Fig. 

 248) occurs on the Rocky Mountain plateau in Utah and 

 Montana. It is an interesting fact in zoo-geography that 

 there are no species of Apus and Lepidunis east of the west- 

 ern plains. Apiis has been found by Siebold to reproduce 

 parthenogenetically. 



The various species of Branchijms end Artemia have no 



Fig. 246.— Shell oiEstherla 

 Belfrageiy enlarged three 

 times. 



