282 ZOOLOGY. 
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. Gouldit Baird (Fig. 238) is very 
rare in Canada and New-England. The shell 
of Limnadia is thin, oval, and there are from 
eighteen to twenty-six feet-bearing segments. 
LL. (Bulimnadia) Agassizii Packard (Fig. 239) 
Ce inhabits small pools in Southern New En- 
gland. The shell of Hstherta (Fig. 241, Zs- 
Fi. 20_Fore. Lveria Belfraget Packard) is sometimes mis- 
‘ig. ‘ore- 
leg of male Aece taken for that of the fresh-water mollusks 
nus. a, hand ; 0, Cyclas and Pisidium. The males of the fore- 
end of body. 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- 
chipus. The females chiefly differ 
from the males in the presence of an g. 241.—Shell of Hetherta 
orbicular egg-sac on the eleventh pair Balrave, enlarged three 
of feet, the sac being a modification of 
two of the lobes of the feet, and containing but a few eggs. 
Apus equalis Packard (Fig. 242, Fig. 244 A, represents the 
larva of a European Apus) inhabits pools in the western 
plains. Lepidurus differs from Apus in having the telson 
spoon-shaped instead of square. JZ. 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 Lepidurus east of the west- 
ern plains. Apus has been found by Siebold to reproduce 
parthenogenetically. 
The various species of Branchipus and Artemia have no 
a 
