54 The Shell-Collector’s Handbook. 
v. ponderosa (Pasc.): Shell very large, more elongated, - 
narrowing towards its posterior extremity, more ventri- 
cose, thicker, brown. 
v. curvirostris (Norm.): Shell smaller, shortened, 
bent, cuneate posteriorily, olive-coloured. 
v. latior (Jeff): Shell broader, shorter, yellowish- 
brown. 
v. rostrata (Zam.): Shell slightly more elongated, 
lanceolate behind, brownish (= VU. rostrata, Lam! Anim. 
Sans. Vert. vi., 1, p. 77). 
v. compressa (Jeff.): Shell broad and flat; upper 
margin raised and curved; posterior side greatly com- 
pressed and attenuated, assuming a beak-like form, and 
having a double ridge and furrow, which runs from the 
beak in the younger state of growth; lower margin 
straight ; lunule broad, and extending between the beaks 
so as to separate them from each other. 
UNIO MARGARITIFER, LINN. 
SHELL elongate-ovate, thick, heavy, rather compressed, 
black brown, strongly striated in the line of growth; um- 
bones excentric, incurved, and generally more or less 
extensively eroded; lunule indistinct and narrow; liga- 
ment very long, and extending to anterior side; anterior 
side rounded ; posterior side gradually sloping, rounded at 
its extremity, and obtusely keeled above; lower margin 
straight; hinge strong; cardinal teeth small, slightly 
compressed, thick, subtriangular-conic, the posterior one 
of the left valve much developed. Animal dirty grey, 
more or less reddish. Length 53 inches; width 23 inches ; 
thickness 1 inch. 
Habitat—Among the gravel and small stones in the 
shallows of quick-running rivers or mountain torrents. 
