122 Art. 6.— M. Yokuyania: 



Palliai sinus almost horizontal, shallow, triangular to semi-ellip- 

 tical in form with the apex blunt. Inner margin finely crennlate. 



The posterior subtruneation of the shell makes it not unlike 

 Chione > gravescens Menke (Syst. Conch. Cab. XI, pi. 1, pi. 25, fig. 

 8) from Australia which, however, has a less number of laminae. 

 The shape of the palliai sinus varies in shape from triangular to 

 semi-elliptical. 



The fossil specimens which are tolerably numerous are all 

 small. The largest which is a right valve is 16,5 millim. in 

 length, 15 millim. in height and 5 millim. in depth. 



Fossil occurrence. — Naganuma Zone (Naganuma). Upper 

 Musashino of Musashi and Shimosa. 



Living. — Japan (according to Dunker); China Sea. 



150. Chione minuta, Yokoyaaia. 

 Pl. VIII. Fig. 14. 



Shell small, moderately thick, tumid, trigonal, as high as 

 long, inequilateral. Anterior margin rounded, posterior end 

 roundly angulate, ventral margin broadly arcuate. Surface radia- 

 tely ribbed; ribs numerous, unequal, straight, separated by about 

 equal interspaces, often with an interstitial riblet towards the ven- 

 tral margin. Besides the radiating ribs, there are*also fine, distant, 

 somewhat lamellar, concentric striae which give the surface a 

 somewhat cancellated appearance. Lunula and area absent. 

 Teeth in the right valve three, the anterior thin and parallel to 

 the antero-dorsal margin, the middle thick and bifid, and neai'ly 

 vertical, the posterior longer and thicker than the anterior, very 

 oblique, and parallel to the postero-dorsal margin. Muscular im- 

 pressions elongated, the posterior a little larger than the anterior. 

 Palliai line indistinct, palliai sinus small, triangular, somewhat 

 directed upward. Inner margin crenulated, the crenulations on 

 the anterior side going up very near the beak. 



A right valve and a broken left valve. The former measures 

 5 millim. in length and height, and '2 millim. in depth. 



This shell has some resemblance to the one described by 



