NO. 2297. BRACHIOPOD GENUS PLATYSTROPHIA—McEWAN. 431 



Platystrophia biforata var. crassa Winchell and Schuchert, Geol. Minnesota, vol. 



3, 1893, p. 458, pi. 33, figs. 55, 56.— Whiteaves, Palaeozoic Fossils, vol. 3, pt. 



3, Geol. Siirv. of Canada, 1897, p. 178. 

 Platystrophia costata Cumings and Mauck, Amer. Journ. Sci., ser. 4, vol. 14, 



1902, p. 14, foot note.— Cumings, Amer. Journ. Sri., ser. 4, vol. 15, 1903. pp. 



38, 122, figs. 26, 27; 32nd Ann. Kept. Dept. Geol. Nat. Res. Indiana, 1908, p. 



914, pi. 35, figs. 6, 6a. 



In 1873 Meek described specimens whicli he had received wrongly 

 labeled as PlaiystropMa dentata Pander. He expressed doubt as to 

 their agreement with the British specimens of PlatystropUa dentata 

 which are described by McCoy. In 1874 James described this form 

 as Platystrophia crassa. 



The hinge line is generally somewhat shorter than the width across 

 the middle; in some specimens it is longer than this width. The 

 lateral slopes are swollen next to the fold and sums and descend 

 rapidly to the free margins. Those of the brachial valve are strongly 

 convex, while those of tlic pedicle valves are concave toward the 

 cardinal extremes. 



James took as his types specimens with high compressed folds and 

 profound sinuses on which the lateral plications were rudimentarv 

 or absent. By far the greater number hxave a compressed, moder- 

 ately elevated fold with lateral plications somewhat weaker than the 

 median plications, but reaching to the free edge. 



In all matm-e and old specimens the inner edges of the lateral slopes 

 of the pedicle valve are elevated to such a degree as to form a pro. 

 found sinus. Gibbosity becomes so pronounced in old specimens 

 that the thickness exceeds the height and may equal or nearly equal 

 the width. 



The shell is narrower and more globose than that of Platystrophia 

 laticosta and Platystrophia cypha. It is somewhat like Platystrophia 

 unicostata crassiformis , new variety, but it has a lower fold than that 

 form. It also has a greater number of plications on the lateral slopes, 

 as there are seven and eight in this species and only tive and six in 

 Platystrophia unicostata crassiformis. By selection it is possible 

 to differentiate, from among numerous specimens, a small number of 

 individuals which are sliortor and thicker than other members of the 

 species. 



It is also possible to differentiate an occasional pauciplicate form 

 with a hinge line decidedly shorter than the other specimens. There 

 are four, rarely five and six, coarse, sharp, and broadly spaced pli- 

 cations on the lateral slopes. Specimens representing this mutation 

 are smaller than other members of the species. 



Occurrence.— MiijsvUle group: All mutations are found in asso- 

 ciation in the Fairmount beds at Cmcinnati, Ohio; Covington, Ken- 

 tucky; and Madison, Indiana, etc. 



Pl€siotypes.~Ca.t. Nos. 35566, 48604, U.S.N.M. 



