Plate XVIII. 



Figs. 1, 2. Pectunculus yessoensis Sow. 1. Left valve, a. Outside, b. Inside. 

 Ökine. 2. Left valve from Motowada. a. Outside, b. Inside, c. 

 Showing depth, p. 168.. 



Figs. 3-6, 7? Pectunculus nipponicus Yok. Different forms of the same species. 

 3, 4. Bound forms. 5, 6. Somewhat triangular forms. 7. Abnormal- 

 ly triangular form? a. Outside, b. Inside, c. Showing depth. 

 Koshiba. p. 168. 



Fig. 8. Pectunculus pilsbryi Yok. Enlarged. Left valve, a. Outside, b. Inside. 

 c. (nat. size) Showing depth. Shimo-Miyata. p. 170.; 



Figs. 9-11. Paralleloden obliquatus Yok. 9, 10. Left valves from Shimo-Miyata. 

 a. Outside, b. Inside. 9c. Showing depth. 10c. View from above. 

 11. Plight valve from Okine. a. Outside, b. Inside, c. Showing 

 depth, p. 170. 



Figs. 12, 13. Limopsis auritoides Yok. 12. Left valve. 18. Eight valve, a. Out- 

 side, b. Inside, c. Showing depth. Nojima. p. 171. 



Figs. 14-16. Limopsis tokaiensis Yok. 14. Plight valve of full-grown specimen. 



a. Outside, b. Inside, c. Showing depth. 15, 16. Left and right 

 valves of Younger specimens, a. Outside, b. Inside, c. Showing 

 depth. Koshiba. p. 172. 



Figs. 17, 18. Limopsis crenata A. Adams. Enlarged. 17. Eight valve, a. Out- 

 side, b. Inside, c. Showing depth. 18. Left valve, a. Outside. 



b. Inside, c. Showing depth. Koshiba. p. 173. 



Figs. 19-21. Limopsis azumana Yok. 19, 21. Somewhat enlarged. Left valves. 

 21. Somewhat elongated form. a. Outside, b. Inside, c. Showing 

 depth. Koshiba. p. 225. 



