Fossils from the M iura. Peninsula and its Immediate North, log 



sculpture consists of many distant concentric elevated striae with 

 interspaces also concentrically finely striated. Beaks small. 

 Lunula lanceolate, bounded by sharp edges, longitudinally striated. 

 Main teeth two, the anterior tooth in the left valve and the posterior 

 in the right valve bind; the anterior lateral of the right valve rather 

 prominent. Anterior muscular impression very much elongated, 

 parallel-sided; posterior muscular impression longly ovate. 



There are two specimens; the one is smaller, but has both 

 valves complete, being 66 millim. long, 08 millim. high and 33 

 millim. thick; the other is larger, but only with the right valve 

 which is 74 millim. long, 67 millim. high and about 21 millim, 

 deep. 



This is a species closly resembling the preceding, the main 

 distinctions being its larger size, the narrowed anterior end, and 

 somewhat more inequilateral shell. Hut of the two specimens 

 above mentioned, the larger one is more like Lucina borealis in 

 form than the other, and there is a doubt whether our specimens 

 are not a variety of this well known Ltnnean species. But at 

 present, I am not able to decide this question, the acquired speci- 

 mens being so few. 



Fossil occurrence. — Koshiba Zone (Koahiba). 



170. Lucina yamakawai, Yokoyama. 

 Pl. X. Fig. 9. 



A single right valve. 



Shell small, moderately thick, tumid, almost equilateral, 

 squarely orbicular, slightly lunger than high; anterior margin 

 rounded, passing gradually into the rounded ventral margin; 

 posterior margin subtruncate, forming an obtuse angle with the 

 sloping postero- dorsal margin as well as with the ventral margin, 

 the angle with the former being sharper than that with the latter; 

 antero-dorsal margin slightly excavated. The surface shows an 

 obtuse keel running from beak to postero- ventral angle, the space 

 behind which is somewhat depressed in the middle. The 

 sculpture consists of fine radiating striae crossed by distant con- 



