INVEETEBEATES. . 523 



marked character, however, is to be observed in its cardinal area, which 

 has its margins almost perfectly parallel, instead of being always 

 slopiug from the beak to the lateral extremities. The same characters 

 and its narrow mesial fold and siuns distinguish it from the variety of 

 S. striatus with somewhat fasciculated costse. It belongs to the sub- 

 genus Trigonotreta. 



Position and locality : Crawfordsville, Indiana, in the shales of the 

 Keokuk group. Lower Carboniferous. 



Spieifee neglectus, Hall. 



PI. 30, Fig. 2 a, and 1 c. 

 SpirifernegUctius, Hall, 1858. Geol. of Iowa, Vol I, Part 2, p. 642, PI. 20, fig. 5. 



"Shell transversely oval, gibbous ; hinge line less than the greatest, 

 width, rounded at the extremities. Dorsal valve convex; mesial fold 

 small at the beak, increasing rapidly towards the front, where it is very 

 prominent, not plicated; beak a little elevated above the hinge, 

 incurved. Ventral valve a little more convex, elevated in the umbonal 

 region, mesial sinus broad and deep, with one broad, faint plication in 

 the middle, and indications of another on each side ; umbo very gibbous ; 

 beak strongly arched ; area high arcuate, its lateral margins rounding 

 gradually on each side ; foramen large, triangular, a little higher than 

 wide. 



Surface marked by about six broad, depressed and rounded, simple 

 plications on each side of the mesial fold and sinus ; concentrically 

 crossed by fine undulating stria? and a few stronger wrinkles of growth.'' 



Position and locality : Warsaw, Hamilton and Nauvoo, Illinois, and 

 Keokuk, Iowa. Keokuk limestone, Lower Carboniferous. 



Spieifee stjborbiculaeis, Hall. 



PI. 30, Fig. 1. 

 Spirifer mborbicularis, Hall, 1858. Geol of Iowa. Vol. I, Part 2, p. BH. 



"Shell suborbicular, length and width nearly equal or somewhat 

 wider than long ; hinge line much shorter than the width of the shell ; 

 cardinal extremities regularly curved. Dorsal valve convex, gibbous 

 above the middle, with the mesial fold becoming defined below the 

 beak, and somewhat prominent at the base. Ventral valve convex, 

 gibbous above the middle, with elevated umbo and beak abruptly 

 incurved over a narrow area, which in length is about equal to half the 

 width of the shell; foramen with the dental lamella? projecting, and 

 partially closed by pseudo-teltidium. 



