410 MEMOIRS OF THE CARNEGIE MUSEUM 



10 inches deep, in yellowisli brown mud. Its color was entirely yellowish brown, 

 mottled lighter and darker, and no trace of olive-green was present. This appa- 

 rentl}' was a stray specimen. 



2. A large male of the first form was found at l>unliar, Fayette County, the 

 ground-color of which was salmon-color (VII, 17), the abdomen lnif(V, 13), irlntish 

 on the sides. The red was brightest on the cheke, with- traces of green- between the 

 tubercles of the hand, and the lower side of the chehe and body were dirty brown- 

 ish yelluw. This is) apparently a case of albinism. 



IV. EC^OLOGY AND GEOGRAPHICAL DISTRIBUTION. 



A. Ecology.-" 



Satisfactory conclusions as to the relation of geographical disti'ibution to the 

 physical conditions of the country can only be expected, if we know all about the 

 ecological laws governing the different species. VC'Ah reference to the seven species 

 of crawfishes present in Pennsylvania, we shall see that the ecological conditions 

 are quite varied, and the single species behave very differently. Thus it is necessary 

 to discuss these facts first, before we attempt to study the distribution. 



Three main types of ecological conditions may be distinguished among t>ur 

 crawfishes. We pos.sess species which generally live in the larger rivers ; (jther 

 species which favor the opposite extreme, preferring the groundwater, where it is 

 not far from the surface, and appears in the shape of springs and swamps; and 

 intermediate between these two conditions is a species which selects the smaller 

 streams for its home. We may conveniently call these "the river species," "the 

 mountain-stream species," and "the Imrrowing species." 



1. TltP River Species. 



Cambariis Jimosns, Caniharns propiiKjims, Cumharns ohscurus. 



Although princi})ally living in the larger rivers of the state, these species ai-e 



not entirely' restricted to them, being able to live in any larger body of water, I'un- 



ning or stagnant, providing it is permanent. Thus these forms, in some cases, go 



'■" " Ecolog}-," the science of the "relation of organisms to external conditions,'' is the oldest term, created by 

 Hieckel (" Oecologie," in " Generelle ilorphuhigie da- Orgauisme," 18(56). The term "Bionomics," which is often used 

 in its place, was first introduced by E. Ray Lankester (in the article: Zoology, in Encyclopaedia Britannica, 9th ed., 

 1888, p. 803), and subsequently, but independently, (as " Binnouiie") by J. Walther (F.inleitung in die Gciiloyie als 

 hislorische IVissensrhaft" 1. Bionomie des Meeres, 1893, p. XX). The term "Oecologie" was revived chiefly by E. 

 Warming, (Plantesamtund. Gruudtrick af den lukologiske Plantegeografi, l'-9o). The term " Ethologie " introduced 

 by F. Dahl (Verh. Ges. Naturf. & jErzte, Bremen, LXIII, 3. 1891. p. 123) has a wider sense, including also what 

 we here call "life-history." 



