172 



The most striking characterist^ics of the new form are i ) its proj,ecting 

 auricular expansions and 2) the very coarse radial striae upon tl^e surfajce oC , 

 both the valves. In all essential points other than these the fossil resenir 

 bles the type species very closely. There is, however, another thing that may 

 be worthy of note ; that is, the somewhat stronger development of thp con- 

 <;entric lines of growth that give rise, with the co-operation of the radial striae, 

 to a sculpture that is characteristic of the variety nspcra Schloth. This is 

 not, however, so conspicuous in this form as in the latter, and the Chinese 

 fossil is more resemblant to the type species than to this variety. 



The Geological Institute of Sendai possesses a great number of specimens 

 of Atrypa reticularis from various localities, either bought or collected by 

 Prot. Yabe in Europe and America. All of these examples have been ex- 

 amined one by one, but none of then has proved to be comparable with the 

 Chinese fossil either in shape or in the sculpture of the shell. This fact con- 

 stitutes another argument in support of the writer's proposing a new varietal 

 name for the Chinese fossil. 



The ventral valve is far less convex than the dorsal, and sometimes is 

 even nearly flat. Hinge-line is very long and straight and projecting beyond 

 the lateral border of the shell, forming somewhat semicircular auricular ex- 

 pansions on either side. The ventral beak is very low, its top being only a 

 little above the hinge line ; it is not crooked. The opposite beak is lower and 

 strongly incurved and lies beneath the ventral beak. No area is observed. 

 If the peculiar auricular expansions are disregarded then the shell is nearly 

 equal in length and breadth, and consequently becomes lenticular. Along the 

 anterior border of the shell there is a flattening on the ventral valve, which 

 -causes an upward fluctuation of the margin. This median flattening, however, 

 is not traceable beyond a short distance from the anterior margin ; on the con- 

 trary, there is a tendency to form a very gentle, hardly recognizable folding 

 which is somewhat obvious in the umbonal region. The dorsal valve is high- 

 -est at the central portion and slopes down rather abruptly in all directions. 

 But it has an inclination to become high along the median line, just as in the 

 case of the opposite valve. This is much rnore conspicuous than in the other 



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