148 THE DEVONIAN OF MISSOURI. 



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



330, fig. 421. 

 1909. Spirifer pennatus Stauffer, Geol. Surv. Ohio, series 4, Bull. 10, pp. 189-190. 

 1911. Spirifer mucronatus Cleland, Wisconsin Geol. Nat. Hist. Surv., Bull. 21, pp. 



80-81, pi. 16, figs. 12-14. 

 1913. Spirifer mucronatus Prosser and Kindle, Maryland Geol. Surv., Middle and 

 Upper Devonian, pp. 187-190, pi. 17, figs. 10-18. 



Hall's description — "Shell more or less gibbous, semicircular, semioval, or triangular 

 in outline; cardinal angles sometimes truncate but usually extended, and often ex- 

 tremely prolonged into mucronate points, giving a length of hinge line two, three, or 

 four times as great as the shell; sides straight or curving, the front straight or concave. 



Ventral valve often scarcely more convex than the dorsal, but in very gibbous 

 forms becoming more unequal, gently curving to -the lateral margins. The beak is small 

 and incurved over the narrow linear area, the mesial sinus is sharply defined, quite to 

 the apex, and limited by angular plications which are stronger than the adjacent ones. 

 The prevailing form of the sinus is shallow and rounded in the bottom; it is sometimes 

 flat and sometimes with a fold in the centre, and again it is angular. 



Dorsal valve moderately convex, sometimes becoming gibbous. The sides are 

 gently curving, and usually flattened towards the cardinal margin; the mesial fold 

 prominent and well-defined, flat or rounded above, sometimes with a median groove and 

 again angulated in the middle. The beak is incurved, and the area extremely narrow, 

 about one-third as high as that of the ventral valve. 



Surface marked by from eight or ten to twenty or more subangular plications on 

 either side of the mesial fold and sinus; the plications are not very prominent but usually 

 well defined, the outer half of the number not reaching the beak, but terminating in the 

 callosity along the area-margin. The plications are crossed by numerous fine lamellose 

 striae, which become crowded together and closely imbricating towards the front of the 

 shell, sometimes presenting several interrupted lines of growth." 



Remarks — The southeastern Missouri specimens are of the ordinary type of the 

 species. Many of the specimens are well preserved. They are common in the St. 

 Laurent limestone and in the sandstone phase of the St. Laurent. The specimens in 

 Walker Museum from the limestone phase were collected 3 miles south of St. Marys and 

 on Little Saline Creek and those from the sandstone phase from 1 */£ miles west of Lithium 

 and from Little Saline Creek. 



Spirifer varicosus Hall 



Description and synonomy on page 102. 



Figures on plates 19, 21, 24. 



Remarks — This is a rare species in the Grand Tower of Ste. Genevieve County. 

 Only four specimens are in the collections of Walker Museum and two of them are 

 doubtful. It seems to be much less common than in the Mineola of central Missouri. 



Family SUESSIIDAE 

 Genus Cyrtina Davidson 



Cyrtina alpenensis Hall and Clarke 

 Plate 35, figures 6, 7 and 8. 



1894. Cyrtina umbonata var. Alpenensis Hall and Clarke, Pal. New York, VIII, pt. 



il, p. 362, pi. 28, figs. 16-20. 

 1897. Cyrtina umbonata alpenaensis Schuchert, Bull. U. S. Geol. Surv., 87, p. 199. 

 1909. Cyrtina alpenaensis Grabau and Shimer, North American Index Fossils, I, p. 



313, fig. 393, d-e. 



