SYRINGOTHYRIS 403 



plane of the valve, while in 8. textus it slopes anteriorly and the angle 

 with the plane of the valve is acute. The delthyrial plate in this species 

 is distinctly keeled longitudinally while in S. textus it is nearly or quite 

 flat upon its outer surface. The species resembles 8. typa in the broad 

 and large muscular impression of the pedicle valve and in the strong pli- 

 cations of the shell which are more nearly equal on the two valves than in 

 many species of the genus. 

 Horizon. Keokuk limestone. 



SYRINGOTHYRIS SOLIDIROSTRIS n. sp. 

 Plate LXX, Fig. 5 



Description. Shell large, wider than long, the greatest width along the 

 hinge-line, the cardinal extremities angular. The type specimens are too 

 fragmentary to give accurate measurements, but one incomplete pedicle 

 valve has the following dimensions: maximum length from beak to front 

 margin 50.5 mm., maximum width along hinge-line 57.5 mm., height of 

 cardinal area 27 mm., width of delthyrium at hinge-line 18.5 mm. 



Pedicle valve obliquely subpyramidal in form, most prominent at the 

 umbo, the surface sloping to the cardinal extremities, the lateral and an- 

 terior margins with a gently convex curvature; mesial sinus non-plicate, 

 originating at the beak, rather sharply defined, of medium depth and 

 rounded in the bottom; the beak obtusely pointed, erect; cardinal area 

 nearly flat, inclined posteriorly from the hinge-line at an angle greater 

 than 90 degrees to the plane of the valve, and increasing with the age of 

 the shell; delthyrium broad, its width two-thirds or more than two-thirds 

 the height; each lateral slope of the valve marked by about 18 strong, 

 simple, rounded plications which originate along the cardinal margin and 

 grow successively smaller towards the cardinal extremities. Internally 

 the rostral portion of the valve is nearly solidified back of the delthyrial 

 plate, the continuous portion of the delthyrial plate is about three-fourths 

 as long from the apex of the delthyrium as the total height of the delthy- 

 rium and is concave transversely, the free extension of the syrinx is rela- 

 tively short and broad, and is attached nearly to its distal extremity to 

 the floor of the valve; the dental lamellae are short and rather thick and 

 diverge much more widely than the lateral boundaries of the mesial sinus ; 

 the muscular scars are broad and deeply impressed, with a distinct, 

 rounded, mesial elevation corresponding with the mesial sinus of the ex- 

 ternal surface of the valve. 



In the condition of preservation of the type specimens the minute sur- 

 face markings and punctate shell structure are obliterated. Bather strong 

 concentric lines of growth are present which are distributed across the 

 entire shell, but become somewhat more crowded anteriorly. 



Remarks. This species has been described from two imperfect pedicle 

 valves, the brachial valve being unknown. It is characterized by the 



