10 Proceedings of the Biological Society of Washington. 



Ameiurus natalis (Le Sueur). — Yellow cat. Occasionally taken in 

 the channel behind Plummers Island. 



Ameiurus nebulosus and A. natalis from this region are not nearly so 

 well differentiated as they are, for example, in Lake Ontario. The 

 information at hand does not show whether or not this is a case of 

 hybridization under the somewhat unnatural conditions of the Plummers 

 Island Channel. 



Schilbeodes insignis (Richardson). — Eed-eyed cat. Occurs in Rock 

 Run, Cabin John Run, the river and canal. A specimen of near the 

 maximum size for the species was taken on hook and line in Sycamore 

 Cove, September 4, 1911. 



Catostomid^. 



Carpiodes cyprinus (Le Sueur). — American carp. Occasional in the 

 river and rare in the canal. 



Catostomus commersonii (Lacepfede). — Yellow sucker. White sucker. 

 Hickory shad. Common everywhere in the river and larger creeks; 

 occasional in the canal. Large numbers ascend Rock Run in March and 

 April. 



Hypentelium nigricans (Le Sueur).— Black sucker. Spotted sucker. 

 Stone roller. Taken in the river, and in Rock, Cabin John and Turkey 

 Runs. Large individuals are caught in Rock Run in spring, and speci- 

 mens are sometimes found in the canal. 



The name Hypentelium which has been used subgenerically seems to us 

 to be worthy of generic rank. Catostomus is distinguished among the 

 suckers by having the air bladder large and divided into two parts. In 

 Hypentelium the air bladder is rudimentary. The cranium of Hypentelium 

 is much shorter and broader than in any species of Catostomus and the 

 pectoral fins are set lower and carried horizontally instead of vertically 

 as in most fishes (see Plate II). Hypentelium is developed as a bottom 

 fish and seems to us to be much farther removed from Catostomus than 

 is Pantosteus. 



Erimyzon sucetta oblongus (Mitchill). — Mountain sucker. Chub 

 sucker. Rare in river and canal. 



Moxostoma macrolepidotum ( Le Sueur) . — Large specimens are caught 

 in Rock Run in April. 



Cyprinid^. 



Cyprinus carpio (Linnaeus). — Carp. Abundant in the river and 

 fairly numerous in canal. The largest specimen from the vicinity of 

 Plummers Island examined was 27 inches long and weighed 7% pounds. 



Campostoma anomalum (Rafinesque). — Two taken in Turkey Run, 

 Va., March 27, 1912. Not hitherto recorded from this region. 



Hybognathus nuchalis Agassiz. Taken only in Turkey Run. 



Setnotilus corporalis (Mitchill). — Our only records are for Cabin John 

 Run. 



Semotilus atrotnaculatus (Mitchill). — Horned chub. Abundant in 

 all the creeks, particularly in their upper courses. Found also in shallow 



