REPORT OF THE STATE PALEONTOLOGIST I903 247 



width and concavity respectively ; that of the pedicle valve is 7mni 

 by 9mm by 3mm. 



This species is very similar to S . c r i s p u s of the Niagara 

 group as shown by a comparison of Hall's figures and the following' 

 measurements : 



^ O JL ^ f^ 



O H J O O 



2 r 5 o ^ 





5 g^W MHg^ 



5'. vanuxemi from Trilobite mountain, N. Y. 



6 S 1.34 2 Brachial valve , . 



^ ' Averasfe size 



7 10 1.43 3 Pedicle valve 



10 12 1.2 5 Pedicle valve very convex 



S. crispus, Niagara shale, Waldron Ind} 

 12 15 1. 2 1 4 Pedicle valve 



11 15 1.36 3 Brachial valve 



S. crispus from Rochester shale, Niagara gorge, N. Y} 



5.5 9 1.64 3 Pedicle valve ") Shells of this size arc 

 4.5 92 2 Brachial valve j very abundant 



As seen from the above comparisons and figures,^' ^ S . vanu- 

 xemi bears a closer resemblance toS. crispus of Waldron 

 than it does to the Niagara gorge species. This similarity is spec- 

 ially noticed in the proportion of length to breadth and in the num- 

 ber of plications. The Waldron shells are also much more gibbous 

 and thus approach S. vanuxemi more nearly than do the 

 Niagara gorge specimens. But the cardinal area is much higher 

 even in the young of all specimens of S . crispus examined 

 than in any of S . vanuxemi. It is thus seen that while S . 

 vanuxemi is apparently much more closely related to the 

 western S . crispus than it is to the eastern, that its possible 

 derivation from the western species could not have been a direct one. 



^These measurements are from specimens in the paleontologic collec- 

 tions of Columbia University, New York. 

 'S. crispus. Pal. N. Y. 2 -.262, pi. 54, fig.3a-k. 

 ^S. vanuxemi. Pal. N. Y. 3:198, pl.8, rig.17-23. 



