156 ^^^- ^- — ^^- Yokoyama; 



247. Carflimn tokttnaffai, Yokoyaiiia. 

 PI. XII. Figs. 4, 5, 6. 



Sliell rather thin, tolerably inflated, suborbicular, a little 

 broader than high, anterior border somewhat more broadly round- 

 ed tlian posterior, slightly inequilateral and oblique. The sculpture 

 consists of about twenty-four broad, elevated, rather flatly topped, 

 finely and indistinctly crenate ribs separated by somewhat broader 

 and deep valleys. Beaks small, approaching. Inner margin 

 coarsely crenate. 



The following are some of the measurements of isolated 

 valves : 



The surface in most specimens is more or less decorticated, 

 the crenate character of the ribs being most marked in such. As 

 to the shape, there is some variation. In some examples both 

 anterior and posterior ends are equally rounded, while in others the 

 posterior is subtruncate. Fig. 4 represents a right valve with such 

 a subtruncate posterior end. It is ovate in shape and somewhat 

 different in appearance from the typical form. I believe it is only 

 an abnormal one, but should it prove to be constant in character I 

 would propose for it the name of var. ovata. The specimen meas- 

 ures 30 millim. in length, 26.5 millim. in height and 10.5 millim. 

 in deptli. The ribs number twenty-three and are to a greater 

 part decorticated. 



The typical form of the species is allied to Cardlum slnense 

 Sowerby (Syst. Conch. Cab. Mart. Chem., Cardium, p. 73, pi. 

 XII, figs. 11, 12) in which, however, the lunula as well as the 

 area are well developed. 



Tokunaga in his "Fossils from the Environs of Tokyo" 

 seems to have mistaken this shell for Cardium callforniense Desh., 

 as can be judged from his figure (pi. Ill, fig. 9). The two species 



