76 THE NAUTILUS. 
rior margin rather short, rather strongly curved; inferior well 
curved, more so in front than behind; posterior margin distinctly 
truncated, with a well marked angle where joining the superior, and 
a less marked, rounded angle where joining the inferior margin; 
anterior end forming a slight but distinet angle situated rather high 
up. Surface very finely, irregularly striated, polished; whitish or 
straw colored, often leaden-grayish on the beaks, or even all over. 
Shell moderately thick, nacre whitish ; muscular insertions not very 
distinct; hinge of essentially the same type as that in Pis. abditum. 
Long. 4:0, alt. 3-4, diam. 2°4 mill.; 4°7: 4:0: 2-9 mill. from another 
place. 
Pis. politum is rather variable in size, and more so in color as 
noted above, but so markedly constant in its several habitats that a 
number of different local forms, or varieties could be described. It 
has some resemblance with Pis. abditum Hald. and Pis. variabile 
Pr.; from the former it is different by its being somewhat smaller, 
comparatively shorter and higher, the beaks being less full, the 
surface finer striated and more polished ; from the latter it is distin- 
guished by its smaller size, the beaks being less full, the antero- 
superior margin less straight, and the angle at the anterior end being 
situated higher up; the shell is thinner and the hinge less strong, 
the coloration different. With all these differences appearing only 
gradual, our Pisidium is a good species beyond a doubt and will 
always be recognized. 
It was found, in May a. ¢., in the outlet of a small peaty swamp 
near New Philadelphia, Ohio, about 200 specimens, in company with 
Pis, abditum, varibile and compressum, all, when fresh, being of a 
remarkably uniform color and appearance; Philadelphia, Pa. 
(Morris Schick) ; Grand Rapids, Mich. (L. H. Streng); Joliet, Ill. 
(Jas. H. Ferriss); Clearwater River, and Dallas Lake, Minn. (H. E. 
Sargent). , 
P. mitium Held. This is not a new species, but new to our 
country. A number of specimens from East Twin Lake, at Charle- 
voix, Michigan, dead shells but in perfect condition, in the collection 
of Mr. Bryant Walker, were, after careful comparison, found to be 
congruent, in shape and appearance, as well as in the hinge char- 
acters, with one of the larger forms of Pis. miliwm from England, so 
that there can be no doubt in their identity. 
New Philadelphia, Ohio, Oct., 1895. 
