14 U. S. BUREAU OF FISHEEIES. 



Scandinavia, and Russia). It is found in North America, under 

 similar conditions, in Lakes Superior and Michigan, down to a con- 

 siderable depth (15U fathoms). It is a delicate transparent creature, 

 about half an inch in length. 



DECAPODA. 



The principal fresh-water crustaceans comprised in this group of 

 particular cultural interest as fish food are the prawns and crayfishes. 

 Prawn. — Of the prawns Palaemonetes is the most important. Two 

 species, Falcmnonetes paludosa and P. exilipes, both from North Caro- 

 lina, have been described but are now considered identical. Palae- 

 monetes has been recorded from Florida, the Illinois River, and 

 Lake Erie. 



For the purposes of this paper the most important contribution to 

 the knowledge of the fresh-water prawn, which is locally known as 

 shrimp, is by Worth (1908). Worth calls it the true shrimp and says 

 it is indigenous to the coastal plain region of North Carolina. It is 



the smallest of fresh- 

 water decapods. It was 

 stated that 136 to 140 in- 

 dividuals were counted 

 to a fluid ounce, from 

 which it was calculated 

 '^ that there were about 



Fig. y. — Prawn: "shrimp." Palwmotietes exiUpea. O OAA in r, i^inf no +n Iron 

 Natural siae. After Ward and Wliipple. Z,ZUU in a pint, as laKen 



in early fall, young and 

 old, with no culling. It is exceedingly abundant, "living in masses 

 amongst water mosses and grasses," which in North Carolina are 

 j)ractically universal on all bottoms. It abounds in creeks, mill 

 ponds, or lakelets formed by river overflow, or in pits along rail- 

 road lines where earth for embankments has been obtained. In 

 the latter the shrimp is landlocked and dependent upon rainfall for 

 its Avater supply. These holes, from 2 to 8 inches deep, are unshaded 

 and subjected to extremes of heat and cold, the temperature ranging 

 from 10° to approximately 100° F. In summer the water even ex- 

 ceeds 100°, and in the severest winters it freezes several inches thick. 

 The overflows from the Roanoke River, from a clay country, are ex- 

 ceedingly turbid, but seem to have no deleterious effect upon the 

 crustaceans. Instead of hibernating or burrowing during freezing 

 weather, the shrimp appears merely to seek depth of water. It can 

 not swim against a strong current. 



Crayfishes. — The crayfishes or crawfishes are the commonest in- 

 land representatives of Decapoda. The rather numerous species of 

 P^urope and North America are comprised in two genera. Potamo- 

 bius includes the European crayfishes and the five siDecies of Pacific 

 slope of North America from California to British Columbia. Cam- 

 barus is restricted to North America east of the Rocky Mountains, 

 Mexico, Guatemala, and Cuba. It contains between 70 and 80 species. 



Crayfishes live in rivers, ponds, lakes, sloughs, etc., and some are 

 more or less terrestrial and some subterranean, living in cave waters. 

 They are mainly carnivorous, their food being smaller animals, dead 

 or alive, but southward an omnivorous species makes serious depre- 

 dations on newly planted fields of corn and cotton. A burrowing 



