ZOOLOGICAL SOCIETY BULLETIN. 



923 



tion of certain other ^Madagascar animals, for 

 example, the true lemurs, which flourish on this 

 and other islands of the Indian Ocean, but not 

 on the mainland. 



The first important work on the North 

 American crayfishes was that of Ha<i;en* in 

 1871. Since that time Faxon and Ortniann have 

 added greatly to our knowledge of the group. 

 Hayf lists eighty-four species, only five of which 

 belong to the genus Astactis, found west of the 

 Rocky Mountains. The remaining seventy-nine 

 belong to Cambanis, found east of the Rockies. 

 Nine sjsecies, plus three varieties, were listed 

 for Mexico, Central America and the West In- 

 dies. More recently several additional species 

 have been described. 



Ortmannl has divided the crayfishes of North 

 America according to their habits into three 

 groups: I, river species; II, mountain stream 

 species, and III, burrowing species. While no 

 sharp distinction can be made between these 

 groups, it is true that many species are confined 

 entirely to larger streams and lakes, others are 

 never found except in small cold streams and 

 springs, while others are entirely burrowing in 

 habit. The burrowing species are often found 

 at considerable distance from any open water, 

 in lowlands where they can have water the year 

 round by digging holes, which, in extreme cases, 

 extend to a depth of three or four feet. Some 

 species, known as chimney builders, deposit the 

 earth brought up in constructing the burrow in 

 a ring of pellets around the opening, sometimes 

 extending to a height of ten to twelve inches 

 and a diameter of twelve to eighteen inches, 

 though usually the piles are much smaller. Ac- 

 cording to Ortmann (1. c, p. 4'2) there is no evi- 

 dent purpose in constructing circular mounds. 

 The crayfish sim])ly adopts the easiest way of 

 getting rid of the dirt removed from the burrow. 

 Each hole contains only one individual, except 

 during the time the young remain with the 

 mother and also at the mating season, when a 

 pair may occupy the same burrow. The holes 

 are often found sealed up by pellets of earth 

 placed at or near the mouth, and this is espe- 

 cially true in winter when they may remain 

 sealed for three or four months. 



Crayfishes are all more or less nocturnal in 

 habit, though some of the species of the larger 

 streams and ponds wander about a good deal 

 during the day and are not at all averse to tak- 



*Memoirs of the Museum of Comp.irntivp Zoology 

 of Harvard College, II, No. 1. 



tSynopsis of the Astacklae of North .\merifa. 

 American Naturalist, December, 1899. 



fCrayfishes of Pennsylvania. Memoirs of the Car- 

 negie Museum of Pittsburgh, vol. II, No. X, 190G. 



FEM.4LE CRAYFISH 



Under side sliowinK abdominid legs or swimmerets. Tlie last 



two pairs of walking legs end in spikes, the others 



have pincers for holding the food. 



lug food in the daytime. Other species confine 

 their activities to the night and lie hidden away 

 under stones or in burrows the rest of the time. 

 Four species found in the United States are 

 blind and inhabit caves. The best known of 

 these is Camharus pellucidus (Tellkampf) of 

 Mammoth Cave, Wyandotte Cave and other 

 caverns of Kentucky and Indiana. The e3'es of 

 crayfishes are compound (i. e., composed of 

 numerous facets) like those of insects and 

 other crustaceans. The facets are arranged in 

 a hemispherical form on the end of the movable 

 eye-stalk, but in blind species the facets are 

 wanting. 



The crayfish can walk in any direction, back- 

 ward, forward or sideways, by means of the 

 thoracic legs, though progress by this means is 

 slow. Especially is this true on land, where, not 

 having the buoyancy they possess in the water, 

 they drag themselves along in a laborious fash- 

 ion. In swimming the crayfish uses his abdo- 

 ment after the same manner as the lobster, and 

 a quick movement of the tail will send him dart- 

 ing backward through the water for some dis- 

 tance. When cornered he will defend himself 

 vigorously with the large pincers, but he usually 



