The Nautilus. 



Vol. VII. MAY, 1893. No. 1 



ILLUSTRATIONS OF NEW SHELLS. i 



TJnio Pilsbryi Marsh, Plate I, figs, 7, 8. 



This species is a member of the plicate group of Uniones. It is 

 a decidedly compressed, oblong shell, black in color, having very 

 distinctly marked lines of growth, which are spaced over the greater 

 part of the disk, but become crowded on the lower margin. It has 

 numerous oblique waves, which generally bifurcate indistinctly 

 toward the posterior-lower end. The waves are more or less cut by 

 short impressed furrows, as in JJ. unduhius, etc. The nacre is white 

 and very thick anteriorly, but in the cavity of the valves and pos- 

 teriorly it is thin and stained with blue and olive-green. The lat- 

 eral teeth are also olive-green. 



It was collected by Mr. Elwood Pleas in the Little Red River, 

 Arkansas, and the original description, by Mr. Wm. A. Marsh, will 

 be found in the Nautilus, V, p. 1. 



TJnio Pilshryi is not closely allied to any other American species. 

 It has a striking resemblance to Unio Leai Gray of China. 



Specimens, including the individual figured, are in the special 

 exhibit of United States shells, formed by the American Association 

 of Conchologists, in the Museum of the Academy of Natural 

 Sciences of Philadelphia. 



^The accompanying plate is reprinted by permission from the Proc. Acad. 

 Nat. Sci. of Philadelphia. 



