30 THE NAUTILUS. 
eroded tract behind it. Length of hole contained two and one-half, 
times in length of shell. Interior bluish-white, the hole callus darker 
at the sides. When resting upona plane surface, the peristome of 
the shell is seen to be very much elevated behind, and but little less 
so in front ; the latero-basal margins strongly curved throughout. 
Length 17%, breadth 9, alt. 5mm. 
Length 16, breadth 94, alt.5 mm. 
Twenty-two specimens collected. This seems a very distinct spe- 
cies; the position and proportions of hole, the long posterior and 
short anterior slope, and the strongly curved basal margins being 
especially characteristic, and unlike other described forms. 
Cyrena luchuana n. sp. 
Shell large, inequilateral, oblong, the anterior end short, broadly 
rounded, posterior end long, produced, and squarely truncated ; 
basal margin gently arcuate, dorsal] margin narrowly rounded at 
the beaks, the anterior slope short and nearly straight, posterior 
slope long, rectilinear. Valves strong, convex, the posterior dorsal 
area flat or concave, bounded by a blunt angle, another obtuse 
angle extending from beaks to lower posterior extremity. Interior 
white, stained with buff-olive on the hinge. Cardinal teeth bifid ; 
anterior lateral very short and strong; posterior lateral long, remote 
from cardinals. Cuticle dull brown, with a yellow under color, 
irregularly wrinkle-striate, lamellose behind, and less so over the 
whole disk. Length 94, breadth 72, diam. 47 mm, 
Yaeyama Island, Loo Choo group (Fr. Stearns). 
Cyrena (papua var. ?) yaeyamensis. 
Shell shorter than the preceding, being less produced posteriorly, 
the posterior surface not so distinctly angular, posterior truncation 
less marked; anterior lateral tooth not so short. Anterior dorsal 
slope of hinge line straight, posterior dorsal slope slightly convex. 
Color and sculpture asin /uchuana, except that there is usually 
some oblique corrugation of the posterior slope. Length 75, 
breadth 63, diam. 36 mm. 
Yaeyama I., Loo Choo group (Frederick Stearns). 
This may prove to be a form of Cyrena papua, or of C. buschii 
Phil. of China, but it is more triangular, with the posterior margin 
more produced. 
Cyrena fissidens n. sp. 
Shell resembling C\. sinuosa as figured by Clessin (Conch. Cab., 
pl. 45, f. 1), but the posterior lateral tooth and corresponding pit 
