406 MISSISSIPPIAN BRACHIOPODA 



the base; each lateral slope bearing about 16 or 18 simple, depressed, 

 nearly obsolete radiating plications which originate along the cardinal 

 margin and become successively smaller towards the cardinal extremities. 

 Internally the hinge-teeth are supported by conspicuous, slightly diverg- 

 ing, dental lamellae which extend beyond the middle of the valve along 

 its inner surface, their divergence being much less than that of the lat- 

 eral margins of the mesial sinus; the delthyrial plate well developed, 

 transversely concave, reaching about half way from the beak to the car- 

 dinal margin. 



Brachial valve subsemicircular in outline, with a broad, rounded emar- 

 gination in front, the greatest convexity probably near or at the front 

 margin on the mesial line, the surface curving more abruptly to the car- 

 dinal margin, somewhat compressed towards the cardinal extremities; 

 mesial fold non-plicate, rounded on top, slightly elevated at the beak, 

 becoming broader and moderately elevated in front ; beak small, incurved ; 

 plications of the lateral slopes simple, depressed, rounded, similar to those 

 of the opposite valve, but very much stronger. 



Surface of both valves marked by minute papilla? arranged in concen- 

 tric rows, about 7 or 8 occupying the space of one millimeter ; the papillae 

 of successive rows are alternate in position, and extending anteriorly 

 from each is a minute groove which terminates at about the line of the 

 next succeeding row of papilla?, taken in their aggregate the grooves give 

 to the surface the appearance of being covered with minute shingles with 

 a papilla at the lower extremity of each. Concentric lines of growth of 

 moderate strength occur at more or less irregular intervals and continue 

 across the cardinal area of the pedicle valve. Shell structure punctate. 



Remarks. This species most closely resembles S. gigas, and in many char- 

 acters the two species do not differ. 8. sampsoni, however, has a propor- 

 tionally higher cardinal area and more narrowly triangular delthyrium, 

 and the dental lamella? are much less widely divergent. The type specimen 

 is a badly crushed example so that the exact angle of the anterior slope of 

 the cardinal area cannot be determined, but it is apparently somewhat 

 smaller than that in S. gigas. The shell surface has been largely destroyed 

 from the specimen, but where it is preserved, it exhibits the typical 

 "twilled cloth" ornamentation of this genus and Syringothyris. 



Horizon. Fern Glen formation and Keokuk limestone. 



PSEUDOSYRINX MISSOURIENSIS n. Sp. 



Plate LXV, Figs. 5-9 ; Plate LXVI, Figs. 11-13 



1894. Syringothyris carteri Keyes, Mo. Geol. Surv., vol. 5, p. 87, pi. 40, 

 fig. 10. 



Description. Shell above medium size, broader than long, the greatest 

 width near the hinge-line, the cardinal extremities narrowly rounded. 



