400 Gould's Descriptions of Shells 
Diameter, longitud. seven eighths of an inch ; vertical four fifths 
of an inch ; transverse three eighths of an inch. 
Inhabits Mazatlan. Col. Jewett. 
This species is so similar to the well known T. carnaria, of the 
West Indies, that it is best described by a comparison with it. 
Its form usually is more rounded; stric less numerous and larger, 
forming a more decided angle on the posterior slope ; so that on the 
disk they are more nearly vertical; and on the anterior slope the 
angle they form is so acute as to render them confused along the 
margin, nor have they any undulations at this border. The interior 
is deep carmine throughout, whereas C. carnaria is more roseate, 
and the border is always white ; cardinal teeth of left valve less 
divaricate. Fig. 38, of Sowerby's Thesaurus, seems to represent 
this shell. 
CYRENA ALTILIS (Pl. XVI. Fig. 5.) 
btri l IH ventricosa, tenue striata, calca- 
, 
T solidiuscula, g + 4 P 
rea, epidermide tenui cinereà induta ; libotiibus à lianis valdé elevatis, de- 
clivitate umbonali angulato; facie dorsali antico cordiformi, excavato, margine 
recto, ad extremitatem citò rotundato; margine dorsali postico arcuato ad apr 
cem subtruncato; limbo marginali interiori violacescente, submargine incarnato. 
Shell solid, obliquely subtriangular, ventricose, calcareous, CO- 
vered with a thin ashy-green epidermis; beaks a little antemedian, 
elevated, pointed, incurved and antrorse ; posterior dorsal slope 
decidedly angular, anterior much less so; disks gibbous ; ventral 
margin regularly arcuate : anterior dorsal aspect cordiform, some- 
what excavate, margin rectilinear, extremity briefly rounded ; pos- 
terior dorsal margin somewhat convexly arcuate and compressed, 
and more broadly rounded than the anterior ; hinge well developed ; 
cavity of beaks profound; hinge margin white, disk bluish white, 
region of pallial impression flesh colored ; margin violaceous, 
simple. 
Long. diam. one and three eighths inches; vertical diam. one 
and a half inches ; transverse diam. one and one fourth inches. 
One specimen is marked “ Mexico," by Maj. Rich; another, 
“ Mazatlan (?) " by Col. Jewett. aig 
Compared with C. solida, with which it is nearly related, it s 
less solid, the surface comparatively smooth, and the epidermis 
smooth, the beaks much more elevated, the umbonal ridge sharper, 
