Natural History of District of Columbia — McAtee 95 



The densely vegetated waters that harbor these fishes are 

 confined to the shallower parts of the main river, and its 

 tributaries from the head of Little River at Analostan Island, 

 downstream. Within the limits of the District fauna and 

 flora, these waters constitute a vegetational unit, charac- 

 terized by the abundance of submerged aquatics, as wild 

 celery (Yallisneria spiralis), waterweed (Philotria cana- 

 densis), and various pondweeds as Naias flexilis, Zanni- 

 cliellia palustris, Potamogeton crispus, P. pectinatus, P. 

 pusiUus, P. perfoliatus. P. compressus, P. amplifolius, and 

 P. robbinsii. Most of these species are restricted to Coastal 

 Plain waters, except as they have obtained a foothold in the 

 canal. The marshes bordering such waters have as their 

 principal elements wild rice, cattails, bulrushes, cord-grass, 

 pickerel weed, spatterdock, Peltandra and Sagittaria. 



Four collecting areas on the Virginia side which share 

 more or less the vegetation above described are Four-mile 

 Run. Hunting Creek, Dyke and Mount Vernon. Wherever 

 there is rank marsh along this stretch of shore, occur the 

 cowbell frog or tink-tank (Hyla evittata) and the least bit- 

 tern (Ixobrychis exilis). Both species go upstream as far 

 as the Little River Marsh. A plant that has about the same 

 range is Isoetes saccharata. 



Four-mile Run has a distinct tidal marsh near the mouth 

 in which all three of these species occur. The low ground 

 about the mouth of the creek and the bordering hills are 

 interesting collecting grounds. Various southern crane- 

 flies have been collected here and St. Elmo in this area is 

 the type locality for a remarkable robber fly (Asilus angusti- 

 pennis^ 8 ) and the sole station in our area for a striking 

 southern species of the same family, namely, Laphria saf- 

 frana. Plants that have been collected here only are 

 Panicum flexile and Paspalum longipedunculatum. 



The old city of Alexandria, a little farther down stream, 

 is principally distinguished, from a naturalists point of 

 view, by harboring various introduced species that have not 

 become established elsewhere. These include Salsola kali, 

 Atriplex hastata, Heliotropium europaeum, Hibiscus syriacus 



68 This has been taken at Beltsville also. 



