Fossils from the Miura Peninsula and its Immediate North. 175 



broadly rounded, but sometimes straight and truncate, or even 

 slightly excavated. Surface with fine close radiating impressed 

 lines crossed by concentric striae of growth. Beaks small and 

 acute. Ligamental pit broadly triangular with the breadth of the 

 hase greater (up to twice) than the height. Teeth usually mure 

 than ten and up to fifteen. Inner margin smooth and sharp. 

 The largest specimen measures 12,5 millim. in height. The pro- 

 portions of the three dimensions, height, length and thickness, are 

 10, 10-8.8, 6.6-5.5. 



This species is very variable in shape, especially in the shape 

 of the anterior margin which, as above said, is sometimes even 

 concave, instead of being convex. Such forms I formerly 

 separated as a new species under the name of Limopsis truncata, 

 but as I am now convinced, they are only abnormal forms of 

 .Limopsis azumana. 



Not rare, especially at Koshiba. 



Fossil occurrence. — Miyata Zone (Motoyashiki in Shimo- 

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

 and Shimosa. 



226. Limopsis adamsiana, Yokotama. 

 Pl. XIX. Figs. 1, 2. 



Only two right valves. They are small, solid, compressed, 

 roundly trigonal, nearly equilateral, slightly longer than high. 

 The anterior as well as the posterior margin is rounded, the 

 anterior somewhat more sharply than the posterior. The ventral 

 margin is broadly arcuate. The surface is water-worn but seems 

 to have been ornamented with radiating lines. Beaks small and 

 pointed. The hinge-line is bent, with about five teeth in the 

 anterior half and about six in the posterior. Ligamental pit 

 triangular, somewhat broader than high. The anterior as well as 

 the posterior muscular impression is bounded by an elevated ridge 

 on the inner side, the posterior being much more elevated than 

 the anterior one. Inner surface with fine close radial lines near 

 the mantle-line. Inner margin smooth. 



