A CONTRIBUTION TO OUR KNOWLEDGE OF THE 

 ANATOMY OF THE FRESH-WATER MUSSELS OF THE 

 DISTRICT OF COLUMBIA 



By Lucy Reardon 



0/ Washingto?i, District of Columbia 



All of the North American fresh-water mussels are contained in 

 the family Unionidae, of which five genera are native to the District 

 of Columbia. These are Lampsilis, Sirophitus, Anodonta, Alasmi- 

 donta, and EUiptio. The genus Lampsilis has four species native to 

 the District of Columbia — L. cariosus Say,i. ochraceus Say,i. radiatus 

 Gmelin, and L. nasutus Say. StropMtus has one local species :/S. 

 undulatus Say. Anodonta has one: A. cataracta Say. Alasmidonta 

 has three: A. undulata Say, J.. Tieterodon Lea, and A. marginata Say. 

 EUiptio is represented by two local species : E. complanatus (Solander) 

 Dillwyn and E. productus Conrad. 



In the following "Anatomical descriptions are given the differences 

 exhibited by five local species, namely, Lampsilis ochraceus, L. nasu- 

 tus, Anodonta cataracta, EUiptio complanatus, and E. productus. 



ANATOMY OF LAMPSILIS OCHRACEUS SAY 

 Plate 1, figs. 1 to 10 



DESCHIPTION OF THE SHELL 



Plate 1, figs. 1, 2, and 4 



The shell is elliptical with full beaks which are sculptured with a 

 few straight, stout ridges. Posteriorly from the beaks a well-devel- 

 oped posterior ridge begins and curving slightly down the middle of 

 the shell ends in a blunt point halfway up the height of the shell. 

 The outside is dull, tawny-brownish, usually smoky and feebly rayed. 



The interior of the shell is pearly gray, iridescent, often growing 

 into a deep rose along the margin of the shell. 



The left valve has two small pseudocardinal teeth in front of the 

 beak cavities and two thin, lateral hinge teeth. The right valve has 

 two pseudocardinals opposite each other (with a pit between) and 

 one high thin lateral. 



No. 2782.— Proceedings U. S. National Museum, Vol. 75, Art. M 



27800—29 1 



