March, 1921.] ' The Canadian Field-Naturalist. 45 



eastern stock, it does not seem that we are Evening Grosbeak, leaving its eastern or 



warranted in- calling it anything more de- western affinities, vespertma or brooksi, 



finite than Hesperiphona vespertina, the open for future consideration. 



THE LARGER FRESHWATER CRUSTACEA FROM CANADA. AND 



ALASKA. 



By Frits Johansen. 



(Continued from Vol. XXXV, page 30) 



III. B. TADPOLE-SHRIMPS. 



This suborder (Notostraca) is distinguish- ance to the animal when digging into the 



ed from the Anostraca by having a broad mud or turning around. The interior 



and flat dorsal shield covering the body, organs are similar to those of the fairy- 



and from the Conchostraca by having a de- shrimps though the heart is shorter and 



pressed body, and the shield single and at- there is a large, paired shell-gland, 



tached at the front, not double (as a clam- Locomotion is accomplished principally 



shell) and confluent with the body dor- by the foliaceous legs similar to those of 



sally. the fairy-shrimps, and also by twistings of 



The "tadpole-shrimps" do not have the the tail. The food consists of small fresh- 

 antennae developed to the extent of the water invertebrates (Entomostraca, etc.), 

 fairy-shrimps and clam-shrimps except in or dead animals (even of its own species) 

 their larval stages, but both pairs are which it catches in the water or by tun- 

 diminutive dwarfed stubs, especially the nelling in the surface of the mud bottom, 

 second pair. The paired eyes are not passing any captured prey along to the 

 stalked, but sessile and placed close to- mouth parts by the aid of the foliaceous 

 gether dorsally near the front edge of the legs. The larvjB hatch in the spring as 

 carapace. The mouth parts are well de- clumsy nauplii or metanauplii from the 

 veloped, and behind them follow a great ripe (red) eggs deposited in the fall 

 number of foliaceous body legs (similar to upon water-plants, etc. ; they differ much 

 these of the fairy-shrimps), of which the less from the adults than the larvae of 

 last (11th) pair in the females form a the two other suborders (fairy-shrimps 

 peculiar flat and rounded pouch (like a and clam-shrimps), having traces of the 

 watch-glass) containing the eggs. The carapace and abdominal segments, and 

 first leg-pair is the longest and ends, with later short cercopods. On the other hand 

 Apns, in three long filaments, used as sen- particularly the second pair of antennae 

 sitive organs by the adults and also as are far longer and more powerful tihan 

 swimming-organs by the younger stages, is the case with the adults, and function 

 Behind the carapace protrude a varying as the principal organs of locomotion, 

 number (1 to 3 dozen) of abdominal seg- During the summer the larvge grow on and 

 ments (the tail), which end in a plate gradually assume the shape and colour of 

 (telson) flanked by two long filaments the adult. In some of the species the fem- 

 (cercopods). The color of the adults is a ales attain a length of several centimeters, 

 brownish green, ^ the carapace and' eyes while the males are somewhat smaller. The 

 being the darkest. These animals thus re- latter are generally far less numerous than 

 mind one forcibly of the marine "horse- are the females and often first make their 

 shoe-crabs" (Limuhis) and as in the latter appearance in the latter part of the sum- 

 there is much movement possible between mer; it is therefore probable that when 

 the shield and the body, of great import- this is the case the eggs the females carry 

 in the beginning of the summer are pro- 



1 That of the larva first orange, later yellow- ^^^^^ parthenogenetically, though it must 



ish 



