Sterki: North American SpH.iiRiiD.E. 471 



132. Pisidium guatemalense sp. nov. 



Mussel of medium size, moderately and rather evenly inflated, of 

 elliptical outlines without any projecting angles; beaks somewhat 

 posterior (two fiftlis from the posterior end), rather small, rounded, 

 slightly projecting over the upper margin; surface glossy, with slight, 

 crowded, irregular stria»; color pale corneous, shell transparent, thin, 

 very fragile; hinge rather short, very slight, plate narrow; cardinal 

 teeth small, the right curved, thin, its posterior end bifid with the 

 shanks divergent and curved downward; the left anterior strongly 

 curved, almost conduplicate, pointed, the posterior oblic}ue nearer 

 the longitudinal line, nearly straight, extending forward to over the 

 middle of the anterior; lamina thin, the right anterior: inner with 

 short, pointed cusp, the outer about half the length, posterior small, 

 rounded, the outer small and short; left anterior and posterior with 

 rather small, abrupt, pointed cusps placed distally; ligament and 

 resilium rather long and slight, uncovered along the median line. 



Long. 5.2, alt. 4.3, diam. 2.7 mm. (100 : 83 : 52). 



It is a precarious thing, with Sphseriidie, to establish a species on 

 one or a few specimens. But these two were exactly alike and 

 apparently normal; the hinge is of such unique formation and the 

 shape so different from others knowm, that there can be no doubt 

 that the species is distinct. 



Habitat.- — Conchas River, Quirigua, Guatemala, collected by Mr. 

 A. A. Hinkley, in whose collection the type specimen is. 



PisiDiA Not Seen by the Writer. 



133. Pisidium tremperi Hannibal. 



Pisidium Irempcri H.a.nxibal, Proc. Aial. Soc, X, 1912, p. 137, PI. VII, fig. 22. 

 San Bernardino Mountains, California. Apparently nediV P. ash muni. 



134. Pisidium arcticum Westerlund. 



Piiidium arcticum Westerlund, Nachrichlsbl. Deulsch. Malak. Gesellsch., 1883, 

 p. 58. 



Habitat. — Port Clarence, Alaska. 



135. Pisidium nivale Westerlund. 

 Pisidium nivale Westerlund, I. c. 



Habitat. — Port Clarence, Alaska. 



