Fossils from the Upper Mnsashiuo of Kaznsa and Shimosa. X25 



Fossil occurrence. — Shito (rare). 



189. Corhula pytjtêiœa, Yokoyama. 

 PI. \'II. Figs. 4, 5. 



Several specimens, but mostly right valves. 



Shell small, thick, swollen, high triangular, somewhat oblique, 

 inequivalve, inequilateral; anterior side a little longer than 

 posterior, anterior border rounded, posterior truncate, postero- 

 ventral angle roundly angular, ventral border broadly arcuate. 

 Surface ornamented with regular concentric grooves. Beaks 

 inflated, with an obtuse edge running to postero-ventral corner. 

 Anterior muscular impression curved and pear-shaped, posterior 

 ovate. Palliai line very shallowly indented, the sinus looking 

 only like a broad crescent. 



A specimen with both valves perfect measures 4.3 millim. in 

 length, 3.6 millim. in height and 2.7 milhm. hi thickness. 



Some of the specimens have the surface rather smooth, a 

 phenomenon probably due to friction. 



Fossil occurrence. — Otake (rather frequent), Kioroshi, Tega. 



1»0. Corhula substriafa, Yokoyama. 

 PI. VII. Fig. 3. 



A single right valve. It is small, thick, ventricose, subqua- 

 drate, inequilateral, with anterior side shorter than posterior, 

 rounded in front and quite truncate behind. The postero-dorsai 

 angle is obtuse, while the postero-ventral is roundly right-angled. 

 Ventral margin broadly arcuate. Surface with coarse irregular 

 concentric grooves. Beaks large and swollen, a sharp edge 

 running from them to the postero-ventral corner with a second 

 but weaker one near the hinge-margin. Between these edges the 

 surface is somewhat excavated. Tootli bluntly pointed. Palliai 

 hne distinct, simple. Length 4 milUm. Height 3.0 millim. 

 Depth 2 millim. 



