i6o 



errecht werden." Moreover, in Scupin's material there is one example which- 

 is hardly separable from the variety, still having a large number of ribs. The- 

 ribs are almost equal in strength to those of Sp. siczac in the neighborhood 

 of the cardinal region. 



For the reason that the area is high and that the sinus becomes relatively 

 wider in the later stage, Scupin decided to call Sp. undccimplicatus a variety 

 of Sp. siczac. The present writer would add to these differences another 

 peculiarity on account of which the material at his disposal is to be identified 

 with the variety, but not with the species itself It is the anterior, tongue- 

 like elongation of the sinus. In either ventral or dorsal view according to the 

 figures of the type secies drawn by Scupin the anterior margin is somewhat 

 straight and appears more or less parallel to the hinge-line (figs. 9 and 10). 

 On the contrary, the variety iindcciviplicnta has its front margin somewhat 

 prolonged just as in the specimen now at hand. The size of the Chinese 

 examples is not very conspicuous and is inferior to figures 9 and 10 of Scupin's 

 work, i. e., to the type species of Sp. ziczac. The characteristics, however, 

 are comparable with the variety rather than with the type species. 

 ' In the Chinese specimens as well as in the figures of the variety drawn by 

 Scupin; the hinge-line seems to slope down somewhat laterally, while it is 

 nearly straight in the pictures of Sp. ziczac s.s. This, however, may not be 

 regarded as a characteristic of any importance, as there seem to be transi- 

 tional cases (for instance fig. 9a of Scupin). 



From what has been said above the characteristics of the Chinese ex- 

 amples are probably well understood by the reader, but for convenience's sake 

 the following description is given. 



Shell tranverse, ventricose, ventral valve being remarkably more gibbous 

 than the opposite, somewhat irregularly pentagonal with rounded angles in 

 ventral view ; hinge-Hne a little inferior to the maximum breadth of the shell, 

 which is just below the former. Cardinal extremities are rounded. Ventral 

 beak quite high and pointed, rather strongly recurved over the area, which also 

 is very high and concave ; there is a delthyrium at the center. The valve is 

 most strongly vaulted at a short distance from the beak. A distinct sinus 

 begins very close to the beak and widens and deepens more or less rapidly 



