.130 Art - 6.— M. Yokoyarna: 



naga from the Upper Musashino of Oji under the name of Cardium 

 braunsi. The specimens from Oji have the surface strongly eroded 

 and worn, which is not the case in ours. 



This species resembles Cardium tuberclatum L. (Syst. Conch. 

 Oab., vol. x, pt. 2, pi. V. fig. 1) of the Atlantic and also Cardium 

 nuttalli Reeve (Conch. Icon., Cardium, pi. 13, fig. 66) of the 

 north-west coast of America in both of which, however, the ribs 

 •are nodulously crenate. There are also some differences in shape. 



Fossil occurrence. — MiyataZone (Kami-Miyata). Upper Mu- 

 sashino of Musashi, Kazusa and Shimosa. 



Family Diplodontidge. 



Genus Diplodonta* Bronn. 



162. Diplodonta usta, (Gould). 



Pl. IX. Figs. 14-16. 



Diplodonta usta. Pilsbkt, Cat. Mar. Moll. Jap., p. 133. Yamakawa, On. Diplodonta (Fel- 

 ariella) usta Gould (Japanese), Jour. Geol.Soc. Tokyo, 1909, vol. 16, p. 482, pl. XIV, figs. 1-10. 



Mysia (Felaria) utta. Goui/d, Otia Conchologica, p. 170. 



Mysia pocifica. Tokunaga, Foss. Env. Tokyo, p. 53. 



Diplodonta trigonula. Brauns, Geol. Env. Tokio, p. 44, pl, VI, fig-. 25 (non D. trigonula 

 Bronn). 



The shell is roundly ovate, somewhat oblique, moderate in 

 thickness and tumidity, inequilateral, the anterior side somewhat 

 shorter than the posterior; anterior and posterior margins rounded, 

 passing gradually both into the ventral and the dorsal margins; 

 sometimes, however, the anteror margin may be subtruncate. Sur- 

 face concentrically and unequally striated. Inner surface with 

 radiating lines and a rib running from beak to the anterior mus- 

 cular impression. The palliai line is very distinct. The teeth are 

 two in each valve, the anterior tooth in the left valve and the pos- 

 terior in the right valve being bifid; the anterior tooth in the right 

 valve is thick and triangular, while the posterior in the left valve 

 is thin and ridge-like. The largest specimen in our possession is 

 a right valve, 35 millim. in length, 32 millim. in height and 9 

 millim. in depth. The proportion of length to height is variable. 

 The late Yamakawa who made accurate measurements in many 



