402 THE CHICAGO ACADEMY OF SCIENCES. 
more or less yellowish-horn. Hinge moderately strong, of the 
same type as in /%s. abditum,; cardinal tooth of the right valve 
moderately curved, its posterior part thickened and with a 
deep furrow; below this tooth, there is a deep groove formed 
by the inferior edge of the hinge list raised; and the same 
formation is in the left valve below the deep groove be- 
tween the twocardinal teeth; ligament comparatively strong.” 
(Sterki.) 
Length, 4.50; height, 3.70; breadth, 2.80 mill. 
“In outline our species has some resemblance with P. var- 
ginicum, by its elongate shape, the beaks situated posteriorly, 
the long and below somewhat sacciform anterior part. But it 
is much smaller, its shell quite thin, the hinge finer, the stria- 
tion finer, and the beaks are much smaller.” (Sterki.) 
Animal; Not known. 
Distribution: Northeastern Maine (Nylander); Kent 
County, Utica, Grand Rapids, Mich.; Columbia, Pa.; Mohawk, 
N. Y.; Clearwater and Mississippi rivers, Minn. (Sterki); Du- 
Page River, Ill. (Ferriss); Lilycash Creek, Ill. (Handwerk); 
Francis Creek, Joliet (Ferriss). ' 
Geological distribution: Pleistocene; Loess. 
Habitat: Found on a muddy bottom in company with 
P. compressum and P. abditum. 
Remarks: This is a rare species and has been found only 
in the western region. It may be looked for from both south- 
ern and western regions. 
157- Pisidium scutellatum Sterki, pl. xxxi, fig. 14. 
Pisidium scutellatum STERKI, The Nautilus, Vol. X, No. 6, p. 66, Oct., 
1896. 
Shell: ‘‘Mussel of medium size, rather high, oblique, 
markedly protracted downward in its anterior part, well 
rounded, rather strongly inflated; beaks much posterior, rather 
large, prominent, rounded; superior margin short, little curved, 
or almost straight, scutum and scutellum well marked, form- 
ing projecting angles; the other margins well curved, or the - 
posterior very slightly truncated, anterior end well rounded, 
or with a slight indication of an angle; surface polished, with 
irregular strize and some coarse lines of growth; shell thin, 
transparent, of a yellowish-horn to amber color, often gray- 
ish or brownish-horn in older specimens, and whitish on the 
beaks; nacre glassy, inner surface microscopically rugulose; 
hinge fine, short, cardinal teeth lamellar, the one in the right 
