THE NATURAL HISTORY SURVEY. 407 
it will always be recognized. It also resembles some forms of 
P. pauperculum Sterki, in size and shape, but its comparatively 
coarse striation will distinguish it at once. /%s. handwerk? is 
not a showy Pisidium, with striking features, but nevertheless 
a good species.” (Sterki.) 
161. Pisidium kirklandi Sterki. Unfigured. 
Pisidium kirklanai STERK1I, The Nautilus, Vol. XIII, p. 11, 1899. 
“Mussel of medium size, somewhat oblique, well inflated 
when mature, very little so in the young, high, rather oval in 
outline; superior margin strongly, inferior moderately curved; 
posterior slightly truncated, passing into the superior by an 
obtuse, rounded angle, antero-superior slightly curved or al- 
most straight, sloping toward the rounded anterior end; scutum 
well, scutellum slightly marked;‘beaks somewhat posterior, 
high and prominent in the mature, low in the young mussel, 
with stout ridges, highest at the posterior and slanting toward 
the anterior ends, slightly sinuous on the outer sides; surface 
with very coarse, rather regular striation, dull, rugulose, straw 
colored in young, slightly grayish in the adult with alight zone 
along the margin; shell rather thick, nacre almost glossy, ap- 
pearing bluish in old specimens, muscle insertions distinct; 
hinge stout, hinge plate broad; cardinal teeth of moderate size, 
rather high up on the plate, the right one angular, its posterior 
plate thickened, with or without a groove; below it is a deep 
excavation; left cardinal teeth: the anterior rather stout but its 
edge acute, the posterior oblique, slightly curved; lateral teeth 
stout, the outer ones of the right valve quite small; ligament 
strong.” (Sterki.) 
Length, 4,00; height, 3.80; breadth, 2.70 mill. 
Animal: Not examined. 
Distribution: Michigan, Illinois and Ohio. 
Geological distribution: Unknown. 
Remarks: “Pts. kirklandi is related to P. compressum Pr., 
and more so to fallax St. From the:former it is at once dis- 
tinguished by the more rounded outlines of the adult speci- 
mens; the young are higher in the anterior part and the mussel 
is nearly square, while the young of compressum are more tri- 
angular; and in the latter the beaks are higher, the (young) 
mussel is of comparatively larger diameter. From P. fallax it 
. differs by its large size, the coarse striation, the shape of the 
ridges and the grayish color.” (Sterki.) 
