Fossils from the Mi uni Peninsula and its Immediate -North. 1 K7 



anterior and posterior ends. Surface with fine dense concentric 

 lines. Inner surface with about sixteen distant radial riblets, 

 most distinct near the ventral margin, at a Little distance from 

 which they are somewhat thicker and knot-like. Ears very un- 

 equal, the anterior being the largest; they are also unequal in 

 both valves, those of the right being much larger than those of 

 the left. They are all ornamented with radial scaly riblets, 

 except the posterior ear of the lefl valve, which is very small and 

 smooth. Byssal notch distinct. 



A perfect specimen with both valves from Kami-Miyata 

 measures 11 millim. in length and height, and 3 millim. in thick- 

 ness. 



A single valve (right?) from Koshiba which I described as 

 Pectcit similis Lasky (Proc. Geol. Soc. Tokyo, vol. XXVIII, no. 

 208, p. 3, pi. I, fig. 1) is, as I am now convinced, an imperfectly 

 preserved specimen of this species. 



A young specimen of the left valve from Shimo-Miyala. only 

 5,5 millim. high does not show the radial riblets of the inner 

 surface. 



This species resembles Pecten distinct us Smith (Challenger 

 Lamellibr., p. 304, pi. XXII, fig. 3) in form, but the latter has 

 the radiating striae on the surface, while the internal costulae are 

 wanting. 



Fossil occurrence. — Miyata Zone (Shimo-Miyata and Kami- 

 Miyata); Koshiba Zone (Koshiba). Upper Musashino of Kazusa. 



202. Pecten miurensis, Yokoyama. 

 Pl. XII. Figs. 2-6. 



Shell large, rather solid, compressed, inequivalve, the right 

 valve more convex than the very flattened left valve, nearly 

 equilateral, roundly ovate in form, somewhat higher than long. 

 Surface with about twenty-live smooth, rounded, radiating ribs 

 separated by intervals of about an equal breadth in which there is 

 a single interstitial riblet with traces of distant scales. Ears un- 

 equal, the anterior being the largest, both ornamented with 

 granular radial riblets. 



