410 MEMOIRS OF THE CARNEGIE MUSEUM 
10 inches deep, in yellowish brown: mud. Its color was entirely yellowish brown, 
mottled lighter and darker, and no trace of olive-green was present. This appa- 
rently was a stray specimen. 
2. A large male of the first form was found at Dunbar, Fayette County, the 
ground-color of which was salmon-color (VII, 17), the abdomen buff (V, 18), whitish 
on the sides. The red was brightest on the chele, with-traces of green between the 
tubercles of the hand, and the lower side of the chelee and body were dirty brown- 
ish yellow. This isJapparently a case of albinism. 
IV. ECOLOGY AND GEOGRAPHICAL DISTRIBUTION. 
A. Ecouoey.*! 
Satisfactory conclusions as to the relation of geographical distribution to the 
physical conditions of the country can only be expected, if we know all about the 
ecological laws governing the different species. With 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 our 
crawfishes. We possess species which generally live in the larger rivers; other 
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 burrowing species.” 
1. The River Species. 
Cambarus limosus, Cambarus propinquus, Cambarus obscurus. 
Although principally living in the larger rivers of the state, these species are 
not entirely restricted to them, being able to live in any larger body of water, run- 
ning or stagnant, providing it is permanent. Thus these forms, in some cases, go 
*! ““ Ecology,’’ the science of the ‘‘relation of organisms to external conditions,” is the oldest term, created by 
Heckel (*‘ Oecologie,’’ in ‘‘ Generelle Morphologie der Organisme,’’ 1866). The term ‘‘ Bionomics,’’ which is often used 
in its place, was first introduced by E. Ray Lankester (in the article: Zoology, in Encyclopedia Britannica, 9th ed., 
1888, p. 803), and subsequently, but independently, (as ‘‘ Bionomie?’’?) by J. Walther (Einleitung in die Geologie als 
historische Wissenschaft”? 1. Bionomie des Meeres, 1893, p. XX). The term ‘‘ Oecologie’’ was revived chiefly by E. 
Warming, (Plantesamfund. Grundtrek af den ckologiske Plantegeografi, 1#95). The term ‘‘ Ethologie’’ introduced 
by F. Dahl (Verh. Ges. Naturf. & Erzte, Bremen, LXIII, 2. 1891. p. 123) has a wider sense, including also what 
we here call ‘‘life-history.”’ 
