82 THE DEVONIAN OF MISSOURI. 



bundles as in S. mineolaensis. The major plications are subequal in size in S. plica/a 

 Hall, while about three plications are much the largest in 5. mineolaensis. 



The specimen figured by Kindle in the 25th Annual Report of the Indiana Depart- 

 ment of Geology and Natural Resources, figure 2, of plate 6, may belong to the Mineola 

 species rather than to S. plicata Hall. 



Occurrence — Mineola of Ralls County. The variation toward coarse plications 

 was common with 5. demissa (Conrad) but seems to have gone so far as to produce 

 well-marked species with distinguishing features other than coarse plications in only 

 a few cases. Three of these were in the Snyder Creek shale and one in the Mineola 

 limestone. 



Stropheodonta navalis Swallow 



Plate 11, figure 7; plate 12, figures 4-8; plate 14, figure 12. 



1860 Strophodonta navalis and subnavalis Swallow, Trans. St. Louis Acad. Sci., I, 



pp. 635. 

 1897. Stropheodonta navalis Schuchert, Bull. U. S. Geol. Surv. 87, pp. 424-425. 



Swallow's description — "Shell rather large, thick semielliptical, carinate, punctate, 

 costate. Ventral valve very convex, obtusely carinated, somewhat flattened towards 

 the lateral margins; strongly arched from the beak to the middle, with a more gentle 

 curve towards the anterior margin, where the carina is somewhat depressed and rounded; 

 beak small, incurved slightly beyond the cardinal border; umbo large, projecting slightly 

 beyond the cardinal border; ears distinctly defined and strongly arched towards the 

 area; area straight, linear, common to both valves and vertically striate. Dorsal valve 

 very concave, closely following the curvatures of the ventral, recurved along the cardinal 

 margin, forming the concave surface of the ears; cardinal line as long or longer than 

 the width of the shell. Surface marked by numerous subirregular, rounded, granular, 

 radiating plications; but few originate at the beak of the ventral valve; the number is 

 increased by subdivisions and implantations. The punctate structure is very obvious 

 where the shell is worn or exfoliated. 



Length, 1.40; breadth, 1.44; depth of ventral valve, .61." 



Supplementary description — The shell is rather thin in small specimens. The flat- 

 tening toward the anterior margin is indistinct to obsolete. The umbo is small in 

 comparison with 5. inflexa Swallow and 5. cymbiformis Swallow. The plications are 

 intermediate in size between S. boonensis Swallow and S. equistriata Swallow averaging 

 fewer than 10 to the centimeter. Some are rounded and some subangular. The 

 dimensions of one average and one large specimen are: Length 28 and 39 mm.; 

 breadth 32 and 42 mm. ; height 15 and 18 mm. The width in each case is along the 

 hingeline, both ends of which are missing. The probable width exceeds the measure- 

 ments by about 5 millimeters. 



This species resembles 5. callawayensis Swallow, from which it differs in greater 

 convexity, carinate pedicle valve, greater length compared to width, and more promi- 

 nent umbo. 



Occurrence — Snyder Creek shale, Montgomery and Callaway Counties. 



Genus Pholidostrophia Hall and Clarke 



Pholidostrophia iowaensis (Owen) 



Plate 11, figure 9 



1852 Chonetes (?) iowensis Owen, Geol Survey Wisconsin, Iowa, Minnesota, p. 584, 



pi. 3a, fig. 7. 

 1867. Strophodonta nacrea Hall, Pal. New York, IV, pt. 1, p. 104, pi. 18, fig. 1. 

 1897. Pholidostrophia iowaensis Schuchert, U. S. G. S. Bull. 87, p. 308. 



