282 



ZOOLOGY. 



ria 



mis. a. hand 



end of body. 



This suborder presents a beautiful series of increasingly 

 complex forms, as Ave ascend from Limnetis to BrancJiipus. 

 In Limnetis the bivalve shell encloses the ani- 

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

 There are from ten to tAvelve feet -bearing 

 segments. L. Gouldii Ilaird (Fig. 238) is very 

 rare in Canada and NCAV England. The shell 

 of Limnadia is thin, oval, and there are from 

 eighteen to twenty-six feet-bearing segments. 

 L. (Enlvmnadia) Agassizii Packard (Fig. 239) 

 inhabits small pools in Southern NCAV En- 

 gland. The shell of Estheria (Fig. 241, Es- 

 ^""^""^ theria Belfragei Packard) is sometimes mis- 

 leg of male Esthe- taken for that of the fresh -water mollusks 

 Cyclas and Pisidium. The males of the fore- 

 going genera have the first pair of feet modi- 

 fied to form large claspers (Fig. 240). 



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. 



These Phyllopods usually swim upon 

 their backs, as in the species of Bran- 

 cliipus. 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 fe\v eggs. 

 Aj)us cequalis Packard (Fig. 242, Fig. 244 A, represents the 

 larva of a European Apus) inhabits pools in the western 

 plains. Lepidurux differs from Apus in having the telson 

 spoon-shaped instead of square. L. Couesii Packard (Fig. 

 243) 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 Lepiilnmx cast of the west- 

 ern plains. Apus has been found by Siebold to reproduce 

 parthenogeneticall v. 



The various species of Branohipus and Art cm in have no 



Fig. 241. Shell oiEsthtna 

 Belfragei, enlarged three 

 times. 



