BRACHIOPODA. 73 



1880. Orthis iowensis White, Second Ann. Rep. Indiana Bureau of Statistics and Geol., 



pp. 501-502, pi. 5, figs. 10-12. 

 1882. Orthis impressa Whitfield, Geol. Wisconsin, IV, p. 326, pi. 25, figs. 13-15. 

 1884. Orthis impressa Walcott, Mon. U. S. Geol. Survey, VIII, p. 115, pi. 13, fig. 13. 

 1889. Orthis propinqua Nettelroth (non Hall), Kentucky Fossil Shells, Monograph 



Kentucky Geol. Survey, p. 43, pi. 16, figs. 1-3, 7-11. 



1891. Orthis striatula Whiteaves (non Schlotheim), Cont. Canadian Pal., I, pp. 218, 

 283. 



1892. Schizophoria Iowensis Hall and Clarke, Pal. New York, VIII, pt. 1, pp 212-216, 

 pi. 6a, fig. 29. 



1892. Schizophoria impressa Hall and Clarke, Ibid, pp. 212-216, pi. 6, fig. 31; pi. 6a, 

 figs. 26, 27. 



1895. Orthis iowensis Keyes, Geol. Survey Missouri, V, pt. 2, p. 62, pi. 38, fig. 6. 



1896. Orthis impressa Kindle, Bull. American Pal., 6, p. 36. 



1897. Schizophoria striatula Schuchert, U. S. Geol. Surv., Bull. 87, p. 375. 



1901. Schizophoria striatula Kindle, Indiana Dept. Geol. Nat. Res., 25th Ann. Rept., 



p. 626, pi. 3, figs. 11, 11a. 

 1909. Schizophoria iowensis and Schizophoria macfarlani Greger, Am. Jour. Sci., 



XXVII, pp. 376-377. 

 1911. Schizophoria striatula Cleland, Bull. 21, Wisconsin Geol. Surv., pp. 93-94, pi. 



19, figs. 1-6. 

 1913. Schizophoria striatula Clarke and Swartz, Maryland Geol. Surv., Middle and 



Upper Devonian, pp. 572-574, pi. 52, figs. 14-18; pi. 53, figs 1 and 10. 

 1913. Schizophoria striatula Prosser and Kindle, Maryland Geol. Surv., Middle and 



Upper Devonian, pp. 170-171, pi. 14, figs 13, 14. 

 Hall's description — "Shell rotund. Dorsal valve very gibbose wider than long, 

 sinuate in front ; hinge-line about two-thirds the width of the shell. Ventral valve moder- 

 ately convex at the sides, somewhat flattened on the umbo, with a broad undefined 

 sinus which becomes deeper towards the front, the margin of the shell being somewhat 

 abruptly incurved; area of moderate height, a little incurved at the beak. 



The surface is very finely and evenly striated, and the texture of the shell is minutely 

 punctate. 



The cast of the dorsal valve shows a strong, somewhat quadrilobate muscular im- 

 pression, limited by strong and widely diverging socket-plates, with the vascular im- 

 pressions somewhat narrow and extending below it to the margin of the shell. The 

 surface of the cast preserves fine even striae. The cast of the ventral valve is broadly 

 sinuate in the middle below, with a triangular or subovate deeply bilobed muscular 

 impression, which is subject to considerable variation in form and proportions." 



Remarks — The Schizophorias from Iowa have usually been identified as 5. iowensis 

 Hall and Clarke. According to Clark and Swartz, 1 the main differences between S. 

 iowensis Hall and Clarke and S. striatula are that the former is smaller, has finer stria- 

 lions, more gibbous dorsal valve, narrow median depression on ventral valve, and more 

 sharply sinuous anterior margin. In the Snyder Creek shale of Missouri this is a very 

 abundant form and specimens may be selected that agree with 5. striatula while others 

 agree with S. iowensis Hall and Clarke, or two of the distinguishing characteristics of 

 one and two of the other may be present on the same shell. 



A large specimen of 5. striatula from Maryland is 30 mm. in length by 40 mm. in 

 width. The largest specimen from the Snyder Creek, in the collections of the Uni- 

 versity of Missouri, is 39 mm. in length by 50 mm. in width. Average specimens are 

 about 25 mm. in length by 30 mm. in width. The striations show considerable varia- 

 tion, the larger specimens having the coarser, and they range from the 5. iowensis 

 Hall and Clarke size to that of S. striatula. The extremely gibbous brachial valve is 



'Upper Devonian of Maryland, p. 573. 



