140 THE DEVONIAN OF MISSOURI. 



Hall's description^"She\l transverse, semioval; hinge line often not quite equalling 

 the greatest width of the shell; cardinal angles rarely a little salient. 



Ventral valve moderately gibbous in the middle, and regularly curving to the 

 front and basal margins; the gibbous portions narrowing towards the hinge line, and 

 the umbo little elevated; abruptly depressed towards the cardinal angles, which are 

 nearly flat and sometimes a little deflected at the extremities. 



Dorsal valve with a concavity less than the convexity of the opposite valve; the 

 cardinal angles flat. 



Area of the ventral valve narrow and distinctly wider in the middle, the exterior 

 margin gently curving; foramen partially closed by a convex deltidium, and the aperture 

 filled by the cardinal process of the opposite valve. Dorsal area linear, half as wide as 

 that of the opposite valve. 



Surface marked by fine subequal striae, which are often alternated in size towards 

 the margin. Of these, from 15 to 20 may be counted near the beak, while from bifurca- 

 tion and intercalation there are from 50 to 60 on the margin, becoming obsolete towards 

 the cardinal extremities. The striae are sometimes sharp and angular, and sometimes 

 rounded; fine concentric striae are visible on well-preserved specimens. The cardinal 

 margin of the ventral valve is furnished with two or three spines on each side towards 

 the extremities, and as many more towards the beak, so that the bases of five can be 

 readily counted, and sometimes six; while there is a minute point on each side of the 

 apex, which may be another spine; and this, if preserved, would give twelve or fourteen 

 spines on the cardinal line." 



Remarks — The specimens from southeastern Missouri are too imperfect to make 

 identification certain. 



Occurrence — St. Laurent limestone of Little Saline Creek, Ste. Genevieve County. 



Chonetes vicinus (Castelnau) 

 Plate 32, figures 4 and 5 



1843. Leptaena vicina Castelnau, Systeme Sil. l'Amerique Septentrionale, p. 39, pi. 



15, fig. 9. 

 1867. Chonetes deflecta Hall, Pal. New York, IV, pp. 126-128, pi. 21, figs. 7, 8. 

 1897. Chonetes vicinus Schuchert, Bull. U. S. Geol. Surv., 87, p. 180. 

 1909. Chonetes vicinus Grabau and Shimer, North American Index Fossils, I, p. 236, 



fig. 287. 

 1913. Chonetes vicinus Prosser and Kindle, Maryland Geol. Surv., Middle and Upper 



Devonian, pp. 155-157, pi. 12, figs. 14-21. 

 Prosser and Kindle' s description — "Shell semi-elliptical; length and width as 

 four to five or eight to nine, but rarely proportionally wider. Ventral valve extremely 

 gibbous, regularly arched, the greatest elevation being about the middle of the length; 

 abruptly depressed towards the cardinal angles, which are flattened, with the extremities 

 deflected to the ventral side; the umbo is slightly elevated above the cardinal margin; 

 cardinal area narrow; the interior shows strong dental lamellae, a somewhat angular 

 median ridge terminates above the middle of the valve, and the surface is finely pustulose 

 in the middle, a little more coarsely pustulose along the deflected line and nearly or 

 quite smooth towards the margins. Dorsal valve deeply concave, but not equaling the 

 convexity of the ventral valve; cardinal area more than half as wide as that of the 

 ventral valve; the interior surface beyond the vascular impressions is covered by elongate 

 papillae, the marks of the striae being scarcely distinct. Surface marked by from twenty- 

 six to thirty-four subangular or sometimes rounded striae which are often irregularly 

 increased by bifurcation or intercalation towards the margin; in those with fewer 

 striae, they are sharper and only half as wide as the interspaces, while in those with a 

 larger number, the striae and interspaces are equal; there is a considerable space at the 

 cardinal angles of each valve destitute of striae." 



