A Monograph of the Species of Pisidium. 365 
growth very fine; color pale yellow with zones of yellow ; 
hinge margin very rounded ; teeth rudimentary. 
Dimensions. Long. 0.22; lat. 0.18; diam. 0.13 inches. 
GEOGRAPHICAL DISTRIBUTION. Greenwich, Washington 
County, N. Y. (Ingolls.) 
OssEnvaTIONs. The outline of this shell is very like that 
of the P. obscurum, perhaps anteriorly rather more rounded. 
Compared to the P. minus,is less elongated, broader and 
much larger. It differs from the P. A4damsii in being less 
inflated, as also less oblique. 
y. X 
17. Pistprum NoTATUM Nobis. 
Cabinet of the B. S. N. H. 
PEL XIE Fig. 20, 91, 22. 
Drscmieriow. Shell small, fragile, not pellucid, inflated, 
Somewhat elongated; margins generally well rounded, not 
approximate ; lines of growth regular, not prominent ; shell 
ornamented with prominent ridges rising from the inferior 
margin upwards ; in some cases the ridges are very regular, 
there being from three to four on each valve, and the same 
distance seems to be preserved between each one; in other 
cases, however, there is neither regularity nor symmetry, and 
the number and the size of the ridges being very variable ; 
color light brown, at times ornamented with a broad zone of 
Yellow on the inferior margin; hinge margin rounded ; teeth 
slight; cardinal teeth single; the anterior lateral tooth visibly 
more prominent than the posterior lateral tooth. 
imensions. Long. 0.19; lat. 0.16 ; diam. 0.12 inches. 
EOGRAPHICAL DISTRIBUTION. Greenwich, Washington 
County, N. Y. (Ingolls.) 
