]^28 -^''^- !• — ^^- Yokoyama : 



The shell is thin, flat, transversely oval, inequilateral with 

 the posterior end somewhat gaping. The area is distinct, bounded 

 in each valve by a sharp edge I'unning from beak to postero- 

 ventral corner. Within the area there is an obtuse ridge dividing 

 .the surface into two longitudinal, somewhat concave parts. Lu- 

 nula present, but indistinct. Beaks very small, approaching. 

 Surface only concentrically striate. Ligamental pit triangular. 

 Palliai sinus large and deep, elliptical, reaching somewhat be- 

 yond the beak. 



The largest specimen is a broken right valve 43 millim. in 

 height. The length, if perfect, would be about 63 milHm. The 

 largest perfect right valve obtained measures 32 millim. in length, 

 20.6 millim. in height and 5.4 millim. in depth, while the largest 

 left measures 31.7 millim. in length, 20.8 millim. in height and 

 5.7 millim. in depth. Rare at all the localities. 



Fossil occurrence.^ — Otake, Shisui, Tega. Oji in Musashi. 



Living. — Central Japan. Puget Sound in Washington. 



1!)5. Maefra dunkei'i, Yokoyama. 

 PI. VIL Fig. 7, 8. 



Shell small, rather thin, moderately convex, triangular in 

 general outline, somewhat longer than high, subequilateral, 

 anterior end sharply rounded, posterior bluntly pointed, antero- 

 dorsal border broadly arched, postero-dorsal very convex, some- 

 what angulate in the middle so as to make the shell appear ob- 

 liquely subtruncate behind, ventral broadly arcuate. Surface 

 smooth bluntly carinated. Palliai sinus moderately deep, finger- 

 like. 



This shell stands in form between Ifactra straminea (Ind. 

 Moll, p. 183, pi. VII, figs. 5, 6) and 31. crossei (Ibid. p. 183, pi. 

 VII, figs. 1-4) of Dunker, being more triangular than the former 

 and higher than the latter. Moreover, it is generally smaller. 



The fossil specimens, which are pretty free|uent, do not attain 

 more than 7 millim. in length, while the living found in the Sea 

 of Sagami are somewhat larger. There is a left valve measuring. 



