406 THE CHICAGO ACADEMY OF SCIENCES. 



species, except some forms of P. abditum Hald.; but it is at 

 once distinguished from the latter species by its comparatively 

 very broad beaks, the more elongated and more regular out- 

 line, the different appearance of its surface, usually the lighter 

 color, the comparatively fine and shorter hinge, and, in the liv- 

 ing animal, by the pink color of the soft parts shining through 

 the shell. It is the only species in which that color has been 

 noticed so far, yet it remains to ascertain whether this be a 

 constant character. But, however that may be, the species is 

 valid. From several places specimens were obtained in com- 

 pany with P. abditum, and at once recognized as distinct." 

 (Sterki.) 



Thus far this species has been found in this area only at 

 Higginbotham's Spring, near Joliet, in the western region. Ad- 

 ditional localities will undoubtedly be found when the streams 

 and springs are more carefully searched. 



160. Pisidium handwerki Sterki. Unfigured. 



Pisidium handwerki STERKI, The Nautilus, Vol. XIII, p. 90, 1899. 



"Mussel small, rather rounded in outline, rather high, 

 moderately inflated; beaks moderately large, somewhat papil- 

 liform; superior margin strongly, inferior moderately curved; 

 posterior rounded or slightly truncated, anterior end rounded 

 or with a slight indication of an angle; surface with dense, 

 almost regular and sharp striae, and with a silky gloss, tops of 

 beaks smooth and shining, slightly flattened; color of epiconch 

 pale to yellowish-horn; shell rather strong, nacre colorless or 

 whitish, hinge stout, strongly curved, plate moderately broad, 

 lateral teeth stout, rather high, short; cardinal teeth small, fine; 

 the right one angular, with the posterior part somewhat thicker, 

 inserted in a longitudinal groove on the hinge plate; posterior 

 cardinal tooth of the left valve rather long, longitudinal, nearly 

 straight, its ends sloping; anterior oblique, quite small or almost 

 obsolete; ligament rather small." (Sterki.) 



Length, 2.40; height, 2.20; breadth, 1.70 mill. (Sterki.) 



Animal: Not examined. 



Distribution: Lilycash Creek, Joliet, 111. (J. H. Handwerk). 



Geological distribution : Pleistocene? 



Habitat: Living in soft mud with P. compressum, etc. 



Remarks: "Probably it has been overlooked in materials 

 from other places, owing to its resemblance to immature speci- 

 mens of some forms of P. compressum Pr. When once known 



