PALAEONTOLOGY OF IOWA. 645 



Spirifer pseudolineatus ( n. s.). 



PLATE XX. FIG. 4. 



SHELL transversely elliptical, length about three-fourths as 

 great as the width, the sides symmetrically rounded : valves 

 about equally gibbous. Dorsal valve with the beak a little 

 elevated above the hinge-line and incurved, marked by a 

 rounded undefined mesial fold which is often scarcely visible 

 above the middle of the shell, and moderately conspicuous 

 on the lower half : lateral portions of the valve regularly 

 curving to the margin. Ventral valve more gibbous above 

 the middle ; mesial sinus shallow, rounded, becoming more 

 defined below, and rarely extending to the beak, which is 

 prominent, attenuated, and incurved over the area : area of 

 moderate height, much shorter than the width of the shell, 

 vertically striated, well defined at its junction with the 

 exterior shell, which curves inwards, occupying a portion 

 of the space. 



SURFACE marked by more or less regular concentric la- 

 mellose folds or wrinkles and radiating striae, extended into 

 long bristleform spines from the edges of the folds, which 

 are strongly punctate when the shell is partially exfoliated ; 

 and when still farther exfoliated, the entire surface is 

 strongly striated. 



This species bears some resemblance to S. lineatus ( MARTIN); but the specimens 

 which have come under my observation are generally broader and less rotund, with 

 a more defined mesial sinus and fold, while the concentric folds and radiating striae 

 are less strongly defined than are represented in the figures of SOWERBT and DB 

 KONINCK. It is clearly a representative of the European species, though perhaps less 

 closely similar than another species in the Chester limestone which is figured on 

 Plate xxvii of this volume. The species which appears to be identical with S. lineatus 

 of Europe, is one having a wide geographical range in the coal measures of the United 

 States. 



Fig. 4. Dorsal view of a specimen of medium size. 



Geological formation and localities. In the Keokuk limestone : Keokuk 

 Iowa ; Warsaw, Illinois. 



