18 ANIMAL EESOURCES OF THE UNITED STATES 



53. ARACHNIDA— Coutinued. 



Useful traits : Destroy noxious insects, (spiders.) 

 Injurious traits : 



Venomous, (scorpions.) 



Parasites, (mites.) 



XI. ARTHROPODS. 



M. CRUSTACEA. (Crabs, lobsters, shrimps, prawns, crawfish, lim- 



noria, fish-lice, lernseans, sand and water 

 fleas, barnacles, horseshoe crabs, &c.) 

 Useful products : 



Foods, (fresh and canned crabs, lobsters, shrimps, prawns, 



crawfish, lobsters.) 

 Baits, (crabs, lobsters, shrimps, prawns, &c.) 

 Manures, (horseshoe crabs.) 

 Useful traits : Skeleton cleaners, (beach fleas, &c.) 

 Injurious traits : 



Parasites on fishes and marine mammals, (barnacles, fish- 

 lice, &c.) 

 Destroy earthworks, dams, &c., (crawfish.) 

 Destroy submerged timbers, (limnoria, &c.) 

 Modes of protection against injurious species. E. 4. 

 Methods of capture. D. 7, 31, 32. 



XII. WORMS. 



55. ANNELIDA. (Sipunculoids, leeches, earth-worms, serpulsB, sea- 



worms, &c.) 

 Useful products : 



Food of aborigines, (earth-worms.) D. 1, 2. 



Baits, (earth-worms, sea- worms.) D. 5. 

 Useful traits : 



Used in surgery, (leeches.) 



Used as barometers, (leeches.) 

 Injurious traits : External parasites of animals, (leeches.) 

 Methods of culture, (leeches.) E. 11. 



56. SCOLECIDA. (Tape-worms and flukes, planarians, nemerteans, 



trichinae, thread- worms, rotifers, &c.) 

 Injurious traits : Internal parasites, (numerous species.) 



