March, 1921. J 



The Canadian Field-Naturalist. 



45 



eastern stock, it docs not seem that we are 

 warranted in calling it anything more de- 

 finite than Hesperiphona vespettina, the 



Evening Grosbeak, leaving its eastern or 

 western affinities, vespertina or brooksi, 

 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- 

 ed from the Anostraea by having a broad 

 and flat dorsal shield covering the body, 

 and from the Conchostraca by having a de- 

 pressed body, and the shield single and at- 

 tached at the front, not double (as a clam- 

 shell) and confluent with the body dor- 

 sally. 



The "tadpole-shrimps" do not have the 

 antennae developed to the extent of the 

 fairy-shrimps and clam-slirimps except in 

 their larval stages, but both pairs are 

 diminutive dwarfed stubs, especially the 

 second pair. The paired eyes are not 

 stalked, but sessile and placed close to- 

 gether dorsally near the front edge of the 

 carapace. The mouth parts are Avell de- 

 veloped, and behind them follow a great 

 number of foliaceous body legs (similar to 

 these of the fairy-shrimps), of which the 

 last (11th) pair in the females form a 

 peculiar flat and rounded pouch (like a 

 watch-glass) containing the eggs. The 

 first leg-pair is the longest and ends, with 

 Apus, in three long filaments, used as sen- 

 sitive organs by the adults and also as 

 swimming-organs by the younger stages. 

 Behind the carapace protrude a varying 

 number (1 to 3 dozen) of abdominal seg- 

 ments (the tail), which end in a plate 

 (telson) flanked by two long filaments 

 (cereopods). The color of the adults is a 

 brownish green, ^ the carapace and eyes 

 being the darkest. Tliese animals thus re- 

 mind one forcibly of the marine "horse- 

 shoe-crabs" (TAmuh(s) and as in the latter 

 there is much movement possible between 

 the shield and the body, of great iraport- 



Ish. 



That of the larva first orange, later yellow- 



anee to the animal when digging into the 

 mud or turning around. The interior 

 organs are similar to those of the fair>'- 

 shrimps though the heart is shorter and 

 there is a large, paired shell-gland. 



Locomotion is accomplished principally 

 by the foliaceous legs similar to those of 

 the fairy-shrimps, and also by twistings of 

 the tail. TJie food consists of small fresh- 

 water invertebrates (Entomostraca, etc.), 

 or dead animals (even of its own species) 

 which it catches in the water or by tun- 

 nelling in the surface of the mud bottom, 

 passing any captured prey along to the 

 mouth parts by the aid of the foliaceous 

 legs. The larvae hatch in the spring as 

 clumsy nauplii or metanauplii from the 

 ripe (red) eggs deposited in the fall 

 upon water-plants, etc. ; they differ much 

 less from the adults than the larvae of 

 the two other suborders (fairy-shrimps 

 and clam-shrimps), having traces of the 

 carapace and abdominal .segments, and 

 later short cereopods. On the other hand 

 particularly the second pair of antennae 

 are far longer and more powerful t/han 

 is the case with the adults, and function 

 as the principal organs of locomotion. 

 During the summer the larvie grow on and 

 gradually assume the shape and colour of 

 the adult. In some of the species the fem- 

 ales attain a length of several centimeters, 

 while the males are somewhat smaller. The 

 latter arc generally far less numerous than 

 are the females and often first make their 

 appearance in the latter part of tlie sum- 

 mer; it is therefore probable that when 

 this is the case the eggs the females carry 

 in the beginning of the summer are pro- 

 duced parthenogenetically. though it m'ist 



