394 Gould's Descriptions of Shells 
sinus. Hinge with a very small triangular ligament pit burrowing 
under the beaks, in front of it a small divaricate tooth, and a well 
marked lateral tooth on each side. 
Long. diam. one inch and one eighth of an inch; vertical diam. 
six eighths of an inch ; transverse diam. half an inch. 
Inhabits Mazatlan. Lieut. Green. 
A remarkably small and solid species, with a very unusual hinge. 
It resembles, in general, small specimens of M. similis, but is more 
triangular and more ventricose, as well as more solid. It is closely 
allied to M. cuneola, Gould. 
DONAX FLEXUOSUS (Pl XV. Fig. 8.) 
T. triangularis, cuneata, undulato-flexuosa, antic? acuta, area postica lata, 
alta, subplanulata, undique striis exilibus profundis, radiantibus insculpta ; 
apice post mediano; angulo umbonali postice carinato ; margine ventra i excur- 
vato ; colore albo vel stramineo, intus interdum postice violacea. 
Shell triangular, cuneate, solid, flexuose, white or straw colored, 
sculptured with very regular, crowded, deep radiating grooves, quite 
distinct posteriorly and gradually disappearing at the anterior mar- 
gin, on the posterior area somewhat roughened by the concentric 
striæ : apex posterior ; valves from the apex to the middle of the 
ventral margin tumid, between this and the anterior end constricted, 
ventral margin correspondingly excurved and incurved ; anterior 
end nasute; posterior umbonal slope sharply carinate ; posterior 
area very broad and nearly flat; basal angle very acute ; interior 
shining white or flesh colored, often tinted at the tip and along the 
posterior edge with violet; lateral teeth quite strong. 
Diameters, longitudinal three fourths of an inch ; vertical half an 
inch ; transverse two fifths of an inch. 
Inhabits Santa Barbara. Col. Jewett. 
One of the most remarkable species of the genus on account of i 
its triangular form, its undulating sides, broad and flat posterior 
area, and deep, regular, crowded radiating grooves. 
DONAX OBESUS (PL XV. Fig.9.) 
Donaz obesus, Gould ; Proc. B. S. N. H., Nov. 1851, IV. 90. 
T. parva, solida, ovato-cuneata, ventricosa, nitida, radiatim leviter striata, 
albidis et fulvidis omnino vel radiatim picta, et plerumque zonis Yo" 
