Fossils from the Upper Musashino of Kaznsa and Shimcsa. 173' 



Fossil occurrence. — Otake, Kamenaii, Tega, Shi to (frequent). _ 

 Oji in Musaslii. 



Living. — Central Japan. 



550. Tliraeid seutafana, Yokoyama. 



PJ. XIV. Pio-s. 17, 18, 



Shell small, thin, longer than high, roundly pentagonal, rather 

 compressed, inequilateral witli anterior side a little longer than 

 posterior, rounded in front, truncate behind. Antero-and postero- 

 dorsal margins almost straight and sloping, ventral very little con- 

 vex, postero-ventral corner roundly angulate. Surface smooth, 

 with an obtuse posterior keel. Beaks small, jiointed, directed; 

 backward. Lunula longly ovate, bounded on both sides by a blunt 

 edge. Palliai sinus large, deep, broadly rounded, not reaching the 

 middle of the shell. Examples are rare. One of the left valves 

 measures 6.1 millim. in length, 4 millim. in height, and 1.3 millim. 

 in depth, while one of the right measures 6.6 millim. in length,, 

 4.(S millim. in height and 1.7 millim. m depth. 



This shell looks like a young Thracia, papyracea, but the 

 beaks are smaller and more pointed, and the outline is more pen- 

 tagonal. 



Fossil occurrence. — Shito. 



Family Poromyidae, 



Genus POUORIYA, Forbes. 



551. Pot'otÈtya fleocuosa, Yokoyama. 



PI. XIV. Figs. 15, 16. 



Shell small, thin, convex, triangularly ovate, longer than- 

 high, inequilateral with anterior side somewhat shorter than pos- 

 terior, rounded in front, somewhat obliquely subtruncate behind, 

 with ventral margin broadly convex. Surface with a blunt posterior 

 carina and a shallow depression in front of it. The sculpture con- 

 sists of minute granules arranged more or less radially and most 

 distinct on the hinder and ventral parts, those on the other parts being 

 often obliterated by friction. Lunula ovate, distinct. Hinge: In, 



