246 THE DEVONIAN OF MISSOURI. 



single plication near the apex, which dichotomizes until at the margin it is represented 

 by 5 or 6 plications. 



Surface on each side of the fold and sinus marked by 15 to 20 broad, flattened, 

 simple ribs, separated by flat interspaces. The ribs decrease in size as the cardinal 

 margins are approached. 



Remarks — This common Oriskany species occurs abundantly in the Little Saline 

 limestone. The plicated fold and sinus are a distinguishing characteristic of the species. 

 The shells do not display so great variability as does the associated Spirifer murchisoni 

 and there seems to be no important differences from the New York examples. 



Horizon — Lower and upper beds. 



Figured specimens No. 27501, Walker Museum. 



Spirifer murchisoni Castelnau 



Plate 65, figures 9-11 



1843. Spinfer murchisoni Castlenau, Essai Syst. Sil. l'Amer. Septent., p. 41, pi. 12, 



figs. 1-2. 

 1859. Spirifer arrectus Hall, Nat. Hist. N. Y. Pal., vol. 3, p. 422, pi. 97, figs, la-lh, 



2a-ai, pi. 430, 1861. 

 1908. Spirifer murchisoni Clarke, Mem. N. Y. State Mus., vol. 9, pt. 1, pi. 177, pi.. 



32, figs. 1-10. 

 1913. Spinfer murchisoni Schuchert, Geol. Surv., Md. Low. Dev., p. 411, pi. 70, figs. 

 1-5. 



Description — Shell of medium size or larger, width greater than length, the greatest 

 width along the hinge line. The most common type is a rather broadly extended shell, 

 with regular curving sides. The dimensions of a complete individual are: length'25 

 mm., width 45 mm. 



Pedicle valve convex, characterized by a fairly wide, shallow, mesial sinus, which 

 flattens out toward the anterior margin. 



Brachial valve equally convex with the pedicle, the middle portion elevated into 

 an acute fold; beak incurved beyond the hinge line. 



Eight or nine strong, regularly rounded plications, with two or three indistinct 

 ones near the cardinal angles are present on each lateral slope of the valves. The inter- 

 vening grooves are also rounded. Surface ornamented by fine, closely arranged, radiat- 

 ing striae, which are crossed by concentric striae. 



Remarks — T*he separate valves usually occur, entire individuals are uncommon. 

 The shells exhibit considerable variation in the size, width and depth of sinus, height of 

 fold, angularity and strength of plications, but these differences do not seem to be 

 constant enough to warrant a division into separate species. In general the Little 

 Saline specimens correspond with the same species occurring in the Grand Greve lime- 

 stone of the Gaspe region. 



Horizon — Lower and upper beds. 



Figured specimens No. 27500, Walker Museum. 



Spirifer cf. varicosa Hall 

 Plate 65, figure 12 

 1857. Spirifer varicosa Hall, Tenth Rept. on the State Cab., p. 130. 

 1867. Spirifer varicosa Hall, Nat. Hist. N. Y. Pal., vol. 4, p. 205, pi. 31, figs. 1-4. 



Description — Two fragmentary brachial valves have been observed which may be 

 compared with this Onondagan species. The strongly elevated mesial fold with flattened 

 summit, and the characteristic surface markings constitute the distinguishing marks of 

 the species. 



Horizon — Upper beds. 



Figured specimens No. 27499, Walker Museum. 



