612 * On the Distribution of Fresh- Water Fishes. — [October, 
Nothonotus, Eucalia, Nototropis, Lepidosteus, 
Peecilichthys, Labidesthes, Cliola, Litholepis, 
Etheostoma, Xenisma, Phenacobius, Polyodon 
Microperca, Zygonectes, Chrosomus, Scaphirhynchops. 
Elassoma, Amblyopsis, Phoxinus, 
Of the genera found in New England, only Salmo, Esos, 
Rhinichthys, and perhaps Amiurus are represented by more than 
one species. From thirty to thirty-five genera occur in the 
waters of the Pacific slope. 
XIX. The larger the river basin, the greater its variety of 
forms, — both generic and specific. Compare the number of 
species inhabiting any of the tributaries of the Mississippi with 
those of any eastern river. Seventy species have been taken in 
the little White River at Indianapolis, representing forty-eight 
genera, twice as many as occur in all the rivers of New En- 
gland. ' 
XX. Other things being equal, a river whose course lies in a 
region of undisturbed stratified rocks or of glacial drift contains 
most genera and species. 
XXI. Conversely, rivers whose courses lie over igneous oF 
metamorphic rocks contain fewest species. Such rivers often 
contain great numbers of individuals. 
XXII. Sources of streams on opposite sides of a high water- 
shed often have species in common which do not occur in the 
lower courses of the same rivers. Some mountain species, as 
Salmo fontinalis and Hybopsis rubricroceus, exemplify this. 
XXIII. Certain species have a compact geographical range, 
occurring in all waters within this range, without apparent re- 
gard to the direction of their flow. Such are Lepiopomus ob- 
scurus, in the Alabama, Tennessee, and Cumberland, and Hybop- 
sis microstomus in the James, Roanoke, Kentucky, Cumberland, 
and Clinch. : 
XXIV. Certain species have a wide east and west range, 3P- 
parently regardless of the course of the rivers, but are bound 
on the north or south by parallels of latitude. 
Eucalia inconstans is found from Western New York to Kan 4 
sas, and northward — but never southward —of a line passing 
about fifty miles south of Lake Erie. Pereopsis guttatus has & 
like range, but its southern boundary is in the Potomac and one 
Lota lacustris is similarly circumscribed. The three y gee 
Lythrurus have each a belt of latitude, — L. eyanocephalus š 
longing to the Great Lakes and Upper Mississippi, L. diple- 
