BRACHIOPODA. 103 



Genus Syringothyris Winch ell 



Syringothyris occidentalis (Swallow) 



Plate 20, figures 3-5; plate 21, figures 1-3; plate 23, figure 1 



1860. Cyrtia occidentalis Swallow, Trans. St. Louis Acad. Sci., I, pp. 648-640 



1889. Cyrtina occidentalis Miller, North American Geology and Pal., p. 343. 



1894. Syringothyris occidentalis Keyes, Missouri Geol. Surv., V, p. 86. 



1897. Cyrtina ? occidentalis Schuchert, U. S. G. S. Bull. 87, p. 199. 



1909. Cyrtia occidentalis Greger, Am. Jour. Sci., XXVII, p. 378. 



1910. Syringothyris occidentalis Schuchert, Am. Jour. Sci., XXX, pp. 223-224. 

 1918. Syringothyris occidentalis Branson, Geology of Missouri, pp. 100-101, fig. 7. 

 1920. Syringothyris occidentalis Greger, Am. Jour. Sci., L, p. 23. 



Swallow's description — "Shell of medium size, semi-conical. Ventral valve high, 

 semi-conical, slightly curved from the beak to the anterior and lateral margins; sinus 

 well defined, very wide and flattened in front; area slightly concave, high and tri- 

 angular — base but little longer than the slightly curved sides; foramen extending from 

 the beak to the cardinal line, much wider at the base, and not closed in the specimens 

 observed; beak pointed and slightly incurved; dorsal valve convex, somewhat quad- 

 rangular, much broader than long; lateral edges rounded towards the cardinal extremi- 

 ties; mesial fold broad and convex in front; cardinal line shorter than the greatest width 

 of the shell. Surface marked with some fifteen or twenty rounded plications on each 

 side of the mesial fold and sinus, and numerous concentric lamellose lines, which often 

 become very conspicuous towards the margins; shell punctate." 



Revised description — Shell wider than long, the greatest width along the hingeline 

 or a little in front of it, height about the same as the length. An average specimen 

 measures 30 mm. wide, 23 mm. long and 24 mm. high, cardinal area 17 mm. high, 

 greatest width of cardinal area 20 mm., width of delthyrium at hingeline 8 mm. 



Pedicle valve high, sinus wide and shallow; cardinal area gently arched, margin 

 angular to subangular, meeting the sides in almost a right angle; each lateral slope of 

 the valve marked by about 16 rather faint plications. The dental lamellae extend 

 about 1/3 the length of the valve. They diverge considerably in passing outward along 

 the sinus and their outer ends are against the third plication from the sinus margin. 

 The delthyrial plate extends about half way down the delthyrium and the syrinx extends 

 only a short distance below. No syrinx is developed excepting at the lowest part of the 

 plate, as shown in figures 12 and 14. The upper part is much like a long delthyrial 

 plate in a Spirifer. Spirifer euryteines Owen, in some cases, has a plate comparable to 

 the upper part of this. The syrinx part is not in contact with the edge of the delthyrium 

 and it seems to be solid. Muscular scars well developed, subovate in outline. The 

 adductor scars narrow and elongate and not sharply distinguished from the diductor. 



Brachial valve moderately convex; fold originating at the beak and widening 

 rapidly toward the margin; cardinal area narrow, practically at right angles to the area 

 of the pedicle valve; beak extending sharply beyond the cardinal margin; plications 

 similar to those on the pedicle valve. The muscle scars are of medium size. They extend 

 about 3 times the width of the fold near the hingeline but are confined to the fold at their 

 anterior ends. The scars are not deeply impressed. 



Remarks — This is the oldest species of the genus that has been described, but 5. 

 n. sp. of this volume is from an older formation. During Middle and Upper Devonian 

 the Spirifers evolved toward high areaed forms and the syrinx was one of the results. 



Occurrence — Generally rare in the Callaway but abundant in some places in Boone 

 and Callaway Counties. 



