than high, being about 4-5 times as long as it is high, with an equilaterally 

 triangular delthyrium. The median sinus on the ventral valve is already 

 very distinctly developed at the top of the beak ; it is prolonged anteriorly in 

 a tongue-like extension and curved up almost vertically in front, showing a 

 large upfold of the margin in front view. Corresponding to the sinus is a fold 

 on the dorsal valve which is likewise distinct throughout the whole length of 

 the shell. On the ventral valve there are two radial ribs extraordinarily 

 wider than the others ; they form the boundaries between the sinus and the 

 lateral portions of the shell. On the dorsal valve, on the contrary, two 

 peculiarly wide and distinct grooves separate the median fold from the alar 

 parts ; these grooves exactly correspond to the thick ribs on the opposite 

 valve. 



Dimensions : — 



Length. Width. Thickness. Height of Area. 



19 mm. 



36 mm. 



8 mm. 



(Ventral) 



4 mm. 



II „ 



20 „ 



5 „ 



( „ ) ca. 



2 „ 



— ca. 



24 



5 „ 



(Dorsal.) 





21 „ 



35 „ 



16 „ 





4.5 ,, (Locality unknown.) 



Remarks : — This variety differs from the preceding one in having a much 

 more elongate hinge-line and consequently much more lineal ventral area. 

 The maximum breadth of the shell is in this form represented by the hinge- 

 line itself, which is not usually the case with the preceding form. The out- 

 line, therefore, of the present variety is somewhat trapezoidal in contradistinc- 

 tion to the lyrate form of the former. The sinus and folds are much less well 

 defined in the present fossil than in Sf. disjiincttis var. sub-arcJiioci. 



Locality : — Between Tou-tang and Wei-ning, Ta-ting-fu, prov. Kwei- 

 chou. Associate fossil is 



Dalmanclla striatula Schlotheim. 



There is' one other more complete example of the species bought at 

 Peking by Prof. Y. Yabe. The locality is of course unknown. 

 Geological Age :— Upper Devonian. 



