408 PROCEEDINOS OF THE NATIONAL MUSEUM. vol. 56. 



broad and low and the sinus broad and shallow. Nine plications 

 occupy the lateral slopes. The hinge line generally equals the width 

 across the middle, but it may be somewhat less than the width. 



Measurements. — 18 mm. along the hinge line, 18.5 mm. wide 

 across the middle, 12.5 mm. high, 8.5 mm. thick, 10 mm. sinal 

 width, 2.5 mm. fold height. 



Occurrence. — Trenton group. Curdsville limestone: Mercer 

 County, Shyrock's Ferry and Bergen, Kentucky; and Crossville 

 Quadrangle, Tennessee. Prosser limestone at Fountain, Minnesota; 

 Jacksonburg limestone, New Jersey. 



Coty2)es.—Csit. Nos. 66093, 66095, U.S.N.M. 



c. SUBGROUP C. 

 PLATYSTROPHIA BRACHYNOTA (Hall). 



Plate 42, ligs. 25-28. 



Delthyris brachynota Hall, Geol. New York, Rept. 4th Dist., 1843, p. 70, fig. 6. 

 Orthis biforata Nettelroth, Kentucky, Foss. Shells, 1889, p. .35, pi. 29, figs. 



18-22. 

 Spirifer bi/oratus var. lynx Hall, Pal. New York, vol. 2, 1852, pi. 22, fig. 1. 

 Orthis lynx Chapman, Canadian Journ., new ser., vol. 8. 1863, p. 199, fig. 185. 



This species is about the size of PJatystropJiia daytonensis, but it 

 always has a shorter hinge line and a greater number of plications 

 on the fold and sinus. After the one plication in the sinus has bi- 

 furcated a lateral plication is added on each of the sinal slopes, 

 while on the fold, the intercalation of the median plication is fol- 

 lowed by the bifurcation of the primary plications. Seven and 

 eight plications occupy the lateral slopes. 



Measurements. — 17.3 mm. along the hinge; 20.4 mm. wide across 

 the middle; 14.5 mm. high; 11 mm. sinal width; 6 mm. sinal depth; 

 3.5 mm. fold height. 



Occurrence. — Clinton group of New York. Brassfield limestone. 

 Nelson County, Kentuck5^ Niagara Group. Reynolds Basin, Niag- 

 ara County, New York. Louisville limestone, Louisville, Kentucky. 



Plesioty pes.-— Cat. Nos. 39046, 51348, U.S.N.M. 



PLATYSTROPHIA REVERSATA (Foenste). 



Plate 42, fig. 23. 



Platystrophia biforata var. lynx forma revermta Foerste. Bull. Sci. Lab. Deni- 



son Univ., vol. 1, 1885, p. 81, pi. 13, fig. 7. 

 Orthis (Platystrophia) biforata (part) Foeuste, Pal. Ohio, vol. 7, 1895, p. 579, 



pi. 25, fig. 8. 



This was described by Foerste as follows: 



Shell attaining a fair size, the dorsal valve a little larger; shell wider than long, 

 with a subquadrate outline; no very gibbous forms have as yet been found; hinge line 

 less than the greatest breadth of the valves; cardinal extremities obtusely angular; 

 lateral margins rather sinuous near the hinge-line, rounding to the front, where it is 



