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points, but differs from it first of all in having a far more prominently pointed 

 erect beak as well as in being smaller and with finer striae and fainter con- 

 centric wrinkles on the surface. The writer, however, infers that it is only a 

 young example of the typical A. dcsquaniata, because, in the smaller examples 

 found in the Chinese material some exhibit exactly the same features. Or it 

 may represent another variety of A. reticularis, if the above mentioned pecu- 

 liarities are shown to be constant. 



There are seventeen specimens of the Chinese form at the writer's dis- 

 posal. They were ail collected by Prof. K. Yamaua of the Kyoto University 

 several years ago at Ning-chang in the province of Shen-hsi. Most of them 

 are quite well preserved, although the surface sculpture is often worn away. 

 The characteristics of the variety are very excellently shown by them 

 collectively. 



The shell is usually a little wider than long and comparatively thin ; 

 sometimes it is as long as it is wide. Both the valves are convex, the dorsal 

 valve exceeding in this respect the ventral valve. The hinge-line is straight 

 and long, but does not represent the greatest latitude of the shell, which is just 

 in front of the former ; as is its habitus, the shell gradually narrows anteriorly, 

 thus taking so to speak an inversely trapezoidal shape. In exceptional cases, 

 however, there are forms that take a circular outline also. The ventral valve 

 is convex around the beak region, the latter pointing out somewhat strongly 

 but not incurving. Toward the margin the ventral valve gradually becomes 

 flattened, and in some cases even a little turned down, so as to form a slight 

 concave portion inside the margin. The area is quite high, showing a fora- 

 men on the top ; deltidial plates are discrete. The front margin is slightly 

 deflected upwards, forming a median flattening or even depression upon 

 the surface which corresponds to the median fold traceable on the middle of 

 the anterior border. 



The donsal valve is far more convex than its opposite, the gibbosity being 

 -especially remarkable along the median line of the shell ; there are narrow 

 flattenings on the two postero-lateral corners. The beak is less pointed and 

 there is no area. Inside the anterior margin the shell forms a saddle on the 



