gI10 QUADRULA 
Quadrula guatemalensis Simpson, Pr. Acad. N. Sci. Phila., 
1900, p. 83, pl. 11, fig. 4; Syn., 1900, p. 796. 
This has a more elongated form than any member of the 
group, but it seems to show rather close relationship to Q. 
quadrata. The general external appearance of the shell and 
its comparatively shallow beak cavities lead me to believe that 
it is rather young. It differs from Q. quadrata in being more 
elongated, and compressed, in being lighter colored behind, in 
the shallower beak cavities. color of nacre and size. 
(QQUADRULA RUDIS Simpson. 
Shell elongated, somewhat rhomboid, rather inflated, very 
solid in front but much thinner behind, with a rather sharp, 
curved posterior ridge, which ends in a blunt point at the base 
line and there is an indication of a faint secondary ridge on 
the posterior slope; dorsal line curved rather regularly from 
the beaks to the post-base; basal line incurved behind; anterior 
end rounded; umbonal region very high, the beaks curved in- 
ward and forward but not approaching, their sculpture seem- 
ing to be nodulous, irregular ridges; lunule well marked and 
passing under the beaks; surface covered with rather close 
pustules, which gradually change at the border of the shell to 
slightly nodulous, irregular sulcations; epidermis brown, the 
only specimen seen nearly decorticated; left valve with three 
rather strong, but illy separated, ragged pseudocardinals, there 
being a deep crater between the lower and anterior teeth; lat- 
erals two, the lower the larger; right valve with one large 
pseudocardinal and one lateral; beak cavities very deep, sub- 
compressed ; dorsal scars in a row at the base of the pseudo- 
cardinals; anterior muscle scars very rough; pallial line deep, 
distant from the border, nacre cream-colored. 
Length 113, height 65, diam. 46 mm. 
Rio Taxtunilha, tributary of Rio de la Pasion, Guatemala 
Quadrula rudis Stmpson, Pr. Ac. N. Sci. Phila., 1900, p. 82 
DENI, hes 2: 
Unto crocodilarum var. rudis von Martens, Biol. Cent. Amer. 
Moll., t901, p. 648. 
