102 THE DEVONIAN OF MISSOURI. 



somewhat strong, rugose, zigzag lines of growth, which are sharply bent backwards 

 as they cross the plications." 



Remarks — This species occurs in the Mineola of Ralls County associated with 

 S. varicosus Hall. None of the specimens is perfect. The distinguishing features are: 

 Plications more angular on subvaricosus than on S. varicosus Hall, cardinal area higher 

 and narrower, entire shell narrower, a well defined angular plication in the bottom 

 of the sinus. A larger series might show all gradations between the forms. 



Occurrence — Mineola of Ralls County. 



Spirifer varicosus Hall 



Plate 19, figure 18; plate 21, figures 4 and 5; plate 24, figures 14 and 15. 



1857. Spirifer varicosa Hall, Teath Rep. N. Y. State Cab. Nat. Hist., p. 130. 



1861. Spirifera varicosa Billings, Canadian Jour., VI, p. 255, figs. 63, 64. 



1863. Spirifera varicosa Billings, Geol. Canada, p. 960, fig. 467. 



1867. Spirifera varicosa Hall, Pal. New York, IV, pt. 1, pp. 205-206, pi. 31, figs. 1-4. 



1883. Spirifera varicosa Hall, Second Rep. N. Y. State Geol., pi. 59, figs. 4-8. 



1884. Spirifera varicosa Walcott, Mon. U. S. Geol. Survey, VIII, p. 136. 



1889. Spirifera varicosa Nettleroth, Kentucky Fossil Shells, Monograph Kentucky 



Geol. Survey, p. 134, pi. 10, figs. 11-20, 23-25. 

 1894. Spirifer varicosus Hall and Clarke, Pal. New York, VIII, pt. 2, pp. 17, 36, pi. 



34, figs. 4-8. 

 1897. Spirifer varicosus Schuchert, U. S. Geol. Survey, 87, p. 408. 

 1901. Spirifer varicosus Kindle, Ind. Dept. Geol. and Nat. Res., 25th Ann. Rept., 



p. 644, pi. 9, fig. 3. 

 1909. Spirifer varicosus Grabau and Shimer, North American Index Fossils, I, p. 325, 



figs. 413, a-c. 

 1912. Spirifer varicosus Kindle, U. S. Geol. Surv., Bull. 508, p. 82, pi. 6, fig. 16. 



Hall's description — "Shell somewhat semi-circular or semi-elliptical; length equaling 

 or less than half the width; hingeline equal to the greatest width of the shell, and -ter- 

 minating in salient angles or mucronate extensions. Surface plicated. 



Ventral valve much the more convex; greatest elevation at the umbo, and regularly 

 curving to the front and lateral margins; mesial sinus strongly defined, rather flat in 

 the bottom; beak slightly arcuate. Area high, nearly flat below and slightly concave 

 towards the apex. 



Dorsal valve moderately convex, with a prominent abruptly elevated mesial fold, 

 which is flattened on the summit and sometimes slightly depressed along the centre; 

 the beak projecting a little above the hingeline, and with a narrow area gently incurved. 



The surface is marked by from eight to ten simple and somewhat abruptly elevated 

 plications on each side of the mesial fold and sinus; these are crossed by strong lamellose 

 imbricating lines of growth, which give a varicose character to the surface, and where the 

 shell is exfoliated the plications are nodose. 



In some specimens, distinct fine radiating striae can be observed. There is often 

 a retral curving of the concentric striae in the centre of the mesial sinus, and sometimes 

 a slight elevation along that line." 



Remarks — This is one of the common species in the Mineola fauna though few 

 good specimens have been collected. All of the specimens are small, the largest measur- 

 ing 24 mm. along the hingeline. The average width is 13 to 15 mm. along the hingeline. 

 The number of plications on either side of the fold and sinus ranges from 8 to 11, most 

 specimens having 8, 9 or 10. The median fold in some cases has a well defined groove 

 that forms two plications, while in some specimens the groove is scarcely distinguishable. 

 Only one specimen is well enough preserved to retain the concentric lines that gave the 

 species its name. The beak of the pedicle valve projects slightly farther back of the 

 hingeline than in ordinary 5. varicosus. 



Occurrence — Mineola of Montgomery and Warren Counties. 



