8 ART. 20. — M. YOKOYAMA. 



that we are dealing liere with the well-known Pholadomya 

 margarilacea reaching from the lowest Paheogene up to the 

 Miocene. The Sakasegawa specimen belongs to forms with 

 coarser ribs, while that from Kawachidami to those with finer ones. 

 The depth at which the Miike specimen was found was 

 401 feet. 



4. Crassatella fusca n. sp. 



PL II. Figs. 1-3, o, 6. 



Shell moderately thick, ovately trigonal, somewhat inflated, 

 very inequilateral, posteriorly attenuated ; posterior border less 

 sharply rounded than anterior ; ventral border broadly rounded. 

 Surface smooth with prominent lines of growth. Beaks bluntly 

 pointed and touching. Lunula ovate, sharply bounded, twice as 

 long as broad. Anterior tooth larger than posterior. 



The specimen represented in fig. la has its dorso-posterior 

 portion flattened by pressure, so that a rounded edge seems to 

 run from the beak to the posterior ventral margin. It is dark- 

 coloured on the surface, as if it had been covered with an 

 epidermis of the same colour. 



In outline this species resembles Crassatella plorahea (Chem.) 

 of the Paris Basin (Deshayes, Descr. Coq. Foss., vol. I, p. 33, 

 pi. Ill, figs. 10, 11) but has a much thinner shell. 



Found at depths of 358 ft., 384 ft. and 650 ft. 



6. Venerieardia nippon ica n. sp. 

 PL III. Figs. 5a, 5b. 



There are several specimens of this very characteristic shell 

 which, however, are more or less badly preserved. 



