NO. 2297. BRACHIOPOD GENUS PLATYSTROPHIA—McEWAN. 415 



Occurrence. — Trenton group : Greendale beds: Pleasant Valley and 

 Winchester, Kentucky. Catheys limestone: Nashville, Mount Pleas- 

 ant, and near Gallatin, Tennessee. 



Plesiotype.— Cat. No. 65914, U.S.N.M. 



PLATYSTROPHIA PRECURSOR Foerste. 



Plate 44, figs. 1-4, 17-20. 



Platystropliia colbiensis precursor Foerste, Bull. Sci. Lab. Denison Univ., vol. 16, 

 1910, p. 57, pi. 41, fig. 1. 



This abundant Upper Trenton fossU is represented by larger speci- 

 mens than are usually found at this horizon. It is a transverse form 

 with a low fold and shallow sinus bearing subequal plications. The 

 lateral slopes are occupied by nine plications. The slopes of the 

 brachial valve are convex in the two-thirds next to the fold, and 

 slightly concave in the one-third next to the cardinal extremes. The 

 slopes of the pedicle valve are convex next to the sinus and become 

 concave next to the cardinal extremes. 



Specimens having the same general aspect occur at various horizons 

 in the MaysviUe and Richmond. Platystrophia suhlaticosta, new 

 species, of the Bellevue and Corryville beds, differs from it in having 

 seven plications on the lateral slopes. Platystrophia laticosta and 

 Platystrophia cypha are thicker and more compressed; they also have 

 dwarfed lateral plications on the lateral slopes of the fold and sinus, 

 while in this species the plications are subequal. Platystrophia pre- 

 cursor is less ventricose and has a greater height than Platystrophia 

 clarksvillensis of the WaynesviUe formation. It has many character- 

 istics in common with Platystrophia annieana, but the latter has a 

 deeper sinus. 



By selection it is possible to differentiate from among numerous 

 specimens of Platystrophia precursor a small number of individuals 

 which have a somewhat higher fold and deeper sinus. For these 

 specuuens the varietal name, profunda (pi. 44, figs. 17-20), is suggested. 



Measurements. — 27.3 mm. along the hinge line, 28 mm. wide across 

 the middle, 18.5 mm. high, 16 mm, thick, 11.9 mm. sinal width, 

 6.5 mm. sinal depth, 2.7 mm. fold height. 



Occurrence. — Trenton group: Cjmthiana limestone: Between Colby 

 and Winchester, and also between MUlerburg and Pleasant Valley, 

 Kentucky. Catheys formation: Nashville, Columbia, three-fourths 

 mile east of Aspen HiU, etc., Tennessee. 



Plesiotypes.—€at. Nos. 34247, 48611, 65893, U.S,N.M. 



PLATYSTROPHU PRECURSOR LATIFORMIS, new variety. 



Plate 44, figs, 5-7. 



It is possible to differentiate from the typical specimens of this 

 species a large number which are thinner and decidedly wider in 

 proportion to the height. 



