2 Proceedings of the Biological Society of Washington. 



Potomac River, the contrast between Little River or Eastern 

 Branch or even the main stream near Washington, with a wealth 

 of water plants, or of the broad shallow stream so characteristic 

 above Great Falls, with the section we are now treating, needs 

 no emphasizing. 



This portion of the river is further strongly characterized by 

 the distribution of the anadromous fishes. Three species of 

 herrings and two of sturgeons ascend to Little Falls but no fur- 

 ther, while the shad, striped bass and white perch enter this 

 section of the river only to be stopped by Great Falls. 



Difficult Run, Va. 



Our plans for collecting in Difficult Run were thwarted, and 

 this is particularly unfortunate as Difficult is the largest creek 

 system in our area. We are able to present only a brief list of 

 species taken near the mouth . The upper course of this stream 

 is the only water in our region known to be inhabited by the 

 brook trout. 



LIST OF FISHES. 

 Lower part Upper part 



Ameiurus catus Salvelinus fontinalis 



Semotilus atromaculatus 

 Rhinichthys atronasus 

 Lepomis auritus 



gibbosus 

 Micropterus dolomieu 



In ponds on the rocky headland just below Difiicult Run sun- 

 fishes are very abundant. In the clear water a school of a 

 hundred or more may be seen scrambling for a single morsel of 

 food. The species noted are Lepomis auritus, L. solis, L. gibbosus, 

 L. cyanellus, and Chaenobryttus gulosus. 



ScoTTS Run, Va. 



About ten miles west of the center of the City of Washington 

 is an irregular ridge of from 400 to 500 feet elevation, whose 

 surficial rocks belong to the Lafayette formation. This ridge 

 has a total length of about 3^ miles and is the source of several 

 of the largest creeks in the region. Here head an important 

 branch of Difficult Run, Scotts Run, Pimmit Run, which joins 

 the Potomac at Chain Bridge, Four-mile Run, emptying above 



