Fossils from the M iura Peninsula and its Immediate North. 277 



length of the posterior side. The one valve measures about 9 

 millim. in length, 5 millim. in height and 1,5 millini. in depth, 

 while the other measures 8 millim. in length, 4,5 millim. in 

 height and about 1,5 millim. in depth. 



This species agrees almost exactly with the one described by 

 Smith under the above name, the only difference being a slightly 

 si h >rtcr shell and a less excavated posterior part of the ventral 

 margin in the Japanese specimens. 



Fossil occurrence. — Miyata Zone (Motowada); Koshiba Zone 

 (Koshiba). Upper Musashino of Kazusa. 



Living. — Off Sydney, New South Wales, in 950 fathoms 

 (Smith). 



228. Leda gordonis, Yokoyama. 

 Pl. XIX. Figs. 4, 5. 



Shell small, rather solid, moderately compressed, transversely 

 elongated, inequilateral, the anterior side being somewhat shorter 

 than the posterior. Anterior margin sharply rounded; posterior 

 margin very obliquely truncate, forming an acutely pointed angle 

 with the weakly concave postero-dorsal margin; the ventral 

 margin arcuate, forming a very obtuse angle with the truncated 

 posterior margin. Surface with two radiating ridges, the one 

 running to the acute upper corner of the posterior margin and 

 sharp, the other going to the lower corner of the same margin and 

 very obtuse, the surface between the two being slightly concave. 

 The sculpture consists of numerous fine concentric grooves, much 

 narrower than the interspaces and making the latter appear like 

 rounded riblets. Beaks small, obtusely pointed. Lunula broad- 

 lanceolate, indistinct. Area long-lanceolate, sharply bounded by 

 the upper radiating ridges of the surface and sublongitudinally 

 striated. Teeth small, numerous, the anterior row about as long 

 as the posterior which occupies about four-sevenths, of the posterior 

 side. Palliai sinus rather deep, finger-like, somewhat obliquely 

 ascending. Length 12 millim.; height 6 millim. ; thickness 4 

 millim. 



