SCHELLWIENELLA 59 



Genus SCHELLWIENELLA Thomas 



Description. Shell resupinate, the pedicle valve flat or concave, the 

 brachial valve convex, the hinge-line equaling, less than or greater than 

 the greatest width of the shell in front, the lateral and anterior margins 

 rounded. Cardinal area of the pedicle valve variable in height, differen- 

 tiated into a primary and a secondary area as in Schuchertella, and with 

 the deltidium closing the delthyrium to the apex. Internally the dental 

 lamellae are short and rather widely divergent, and a median septum is 

 absent. The brachial valve is convex, often strongly so, with no cardinal 

 area. 



Remarks. S. in flat a may be considered as a typical American representa- 

 tive of this genus, it being a species in which both the resupinate shell and 

 the short and widely divergent dental lamellae have been clearly recog- 

 nized, these two characters being the essential features by means of which 

 members of this genus may be differentiated from Schuchertella. In prac- 

 tice the resupinate form of the shell, viz., the concave pedicle valve, will 

 doubtless be most commonly used for distinguishing the genus. Among 

 the examples studied in which the characters of the dental lamellae can be 

 determined there seems to be some variation in the strength of their de- 

 velopment, in some instances these lamellae being but little or not at all 

 different from those of Schuchertella. The two genera are closely allied 

 and it is not surprising that there should be a more or less complete 

 intergradation in the character of the dental lamella 3 , but in no case among 

 the specimens here studied has there been any hesitation as to the genus 

 in which any one should be placed on the basis of the form of the pedicle 

 valve. 



SCHELLWIENELLA INPLATA (White and Whitfield) 

 Plate IV, Figs. 7-12; Plate LXXXIII, Fig. 11 



1862. Streptorhynchus inflatus White and Whitfield, Proc. Boston Soc. Nat. 



Hist., vol. 8, p. 293. 

 1877. Streptorhynchus inflatus Hall and Whitfield, U. S. Geol. Expl., 40th 



Par., vol. 4, p. 253, pi. 4, fig. 3. 

 1883. Streptorhynchus cequivalvis Hall, Rep. N. Y. State Geol., for 1882, 



pi. (11 A) 42, figs. 24, 25. 

 1892, Orthothetes inflatus Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 9A, 



figs. 24, 25. 

 1901. Orthothetes inflatus Weller, Trans. St. Louis Acad. Sci., vol. 11, 



pp. 181 and 195, pi. 16, figs. 2-3, and pi. 19, figs. 10-12. 



Description. Shell concavo-convex, of medium size or larger, usually 

 subelliptical in outline and broader than long with the greatest width 

 near or posterior to the mid-length, the hinge-line a little shorter than the 

 greatest width, the cardinal extremities obtusely angular or a little 

 rounded. The dimensions of a nearly complete example, one of the co- 



