360 A Monograph of the Species of Pisidium. 
Dimensions. Long. 0.15 ; lat. 0.14; diam. 0.09 inches. 
GEOGRAPHICAL DISTRIBUTION. Columbia, Lancaster County, 
Pennsylvania, (Haldeman.) 
Osservations. ‘This species seems to be very closely 
allied to the P. minus; on comparison, however, it is found 
to be more ventricose, longer in latitude, and shorter in longi- 
tude; the beaks are more terminal, the marginal outline is 
more rounded, the color is different, and it is on the whole a 
smaller shell. 
ompared to the P. dubium, it is more elongated, less ob- 
lique, less heavily striated, much smaller, and of a different 
color Owing to its habits of burying itself in the ground a 
foot or more, it is generally covered with a coating of light 
mud. Found plentifully. 
f^ 
11. PisiprUM minus Stimpson. 
Cabinet of the B. S. N. H. 
Pl. XH. Fig. 5, 6, 7. 
Cyclas minor. Apaws and Micuets. Bost. Jour. Nat. Hist. IV. 39, 
pl. iv. fig. 2. 
Pisidium minus, Stimpson. Stimp. N. Engl. Moll. 16. 
Description. Shell ovate, elongated, fragile ; margins 
well rounded, somewhat oblique, very finely striated ; beaks 
prominent, two fifths of the distance from one extremity to 
the other; umbones and discs tumid; posterior and hinge 
margins slightly rounded ; color uniform light yellow ; cardi- 
nal teeth small, united ; lateral teeth well developed. - 
Dimensions. Long. 0.15 ; lat, 0.15; diam. 0.11 inches. 
Grocrarnicar pisrrieution. Portland and Monmouth, 
Me. (Adams and Mighels.) Augusta, Me. (Nobis) Wey- — 
