21 



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 (PI. XV. Fig. 8.) 



T. triangularis, cuneata, undulato-flexuosa, antice acuta, area postica lata, 

 alta, subplanulata, undique striis exilibus profundis, radiantibus insculpta 

 apice post mediano ; angulo umbonali postice carinato ; margine ventrali 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 

 striae : 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. Jewet.t. 



One of the most remarkable species of the genus on account of 

 its triangular form, its undulating sides, broad and flat posterior 

 area, and deep, regular, crowded radiating grooves. 



DONAX OBESUS (PI. XV. Fig. 9.) 

 Donax obesus, Gould ; Proc. B. S. N. H., Nov. 1851, IV. 90. 



T. parva, solida, ovato-cuneata. ventricosa, nitida, radiatim leviter striata. 

 coloribus albidis et fulvidis omnino vel radiatim picta, et plerumque zonis vio- 



