PALEONTOLOGY OF IOWA. 647 



Spirifer propinquus ( n. s.). 



VENTRAL valve triangularly pyramidal : beak much eleva- 

 ted, not arched ; sinus well denned, deep, abruptly curving 

 in the bottom ; area plane, the height equalling one-third 

 the width of the shell : width of foramen, at base, about 

 three-fifths the height; exterior sloping abruptly from the 

 beak towards the base. 



SURFACE marked by twenty-four or more simple plications 

 on each side of the sinus. Structure minutely striato-punc- 

 tate, varying with degree of exfoliation. 



This shell has the general form of <S. subcuspidatus; but the sinus is deeper, the 

 area entirely flat, and the number of plications more numerous. I have not yet ob- 

 served intermediate forms which will justify the union of this and the preceding 

 species, though they are nearly allied. 



Geological formation and locality. This species occurs with the preceding 

 in the same localities. 



Spirifer ( n. s.). 



There is in my collection, from the same geological horizon, another species re- 

 sembling the preceding, but more gibbous, the valves being longitudinally more 

 curving and the area concave. It is associated with a species bearing much resemblance 

 to Spirifer attenuatus ; but which is probably a distinct species, with narrower area 

 and more numerous plications. 



Spirifer striatus? var. 



There is in the Keokuk limestone a species resembling the S. striatus ; but the 

 area is less linear and does not extend to the extremities, which are rounded : the 

 sinus is very broad, not defined at its margins, and, together with the mesial fold 

 and lateral plications of the shell, covered by somewhat unequal bifurcating plica- 

 tions, which are themselves covered by fine radiating striae. 



Spirifer lo<>aiii (n. s.). 



PLATE XX. FIG. 7; and PLATE XXI. Fio.l a, b, and Fio. 2. 



SHELL large, transverse, semielliptical ; length and width 

 nearly as three to four, gibbous. Dorsal valve gibbous in the 

 middle, depressed towards the cardinal extremities, and 



