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. Pis. handwerki is 

 not a showy Pisidium, with striking features, but nevertheless 

 a good species." (Sterki.) 



161. Pisidium kirklandi Sterki. Unfigured. 



Pisidiiim kirklandi STERKI, 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 a light 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 upon 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. 



Distribiition : Michigan, Illinois and Ohio. 



Geological distribution : Unknown. 



Remarks: "Pis. kirklandi is related to P. compressbm 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.) 



