HIGHER CRUSTACEANS (MALACOSTRACA) 839 



the caves. The fifth of the blind species is C. acherontis, found in 

 caves in Florida. This belongs to the subgenus Cambarus, and is 

 a member of a rather highly advanced section of the subgenus 

 which is common on the coastal plaiji, ajid is to be regarded as a 

 more recent addition to the cave fauna. 



The economic value of the fresh-water Malacostraca is very 

 different in the different groups. While the isopods, amphipods, 

 and Mysidacea are small, the decapods are larger, but also of these 

 the Atyidae and certain Palaemonidae attain only a medium 

 size. These groups naturally have only an inferior value for man, 

 and are generally overlooked and neglected. Of the larger forms, 

 certain species of Palaemon (prawns, also called shrimps), and the 

 crajrfishes have attracted attention, and are used by man, pri- 

 marily as food. Although this is generally the case in Europe and 

 with a number of tropical forms, in North America they are not 

 very popular, and are only occasionally eaten; yet there is no 

 doubt that Potamobius and Cambarus are to be regarded as part 

 of the natural food supply of this country. Other uses, for instance 

 as fish bait, should be mentioned incidentally. 



On the other hand, some kind of damage or injury done to man 

 or man's work has also been noticed in so far as certain burrowing 

 species are liable to damage dams or levees, or to interfere with 

 farming operations. The latter species are also reported to be 

 injurious to crops, chiefly to sprouting plants. 



In the general economy of nature, all the higher crustaceans 

 perform a twofold task. First, on account of their general habit 

 of devouring masses of decaying vegetable and animal matter, 

 they are to be counted among the scavengers, and second, they 

 themselves serve as food for other animals. They are most impor- 

 tant as fish-food, and even the larger forms are eaten by the larger 

 fishes. In addition, a number of other creatures feed upon them 

 (amphibians, water snakes, birds, and certain mammals). 



Collecting Malacostraca is comparatively easy: the chief thing 

 is to ascertain their whereabouts. This is done along the banks 

 of streams, ponds, or lakes by turning over stones or logs, by 

 investigating overhanging banks, or examining bunches of water 



