80 BRACHIOPODS. 



than it really is. At first glance it then appears strikingly like 

 S. logani Hall, but that form is a much heavier shell, has a 

 hinge-line very much longer, a lower cardinal area, and coarse 

 radiating costse. While probably closely related to 8. grimesi 

 genetically, 8. logani seems to be sufficiently distinct to need a 

 separate specific designation. So far as is known, it has not 

 been found below the Keokuk limestone. 8. grimesi as it oc- 

 curs in the Kinderhook is still lighter in weight, has a still 

 shorter hinge-line and finer ornamentation than the typical ex- 

 amples of the Burlington. The species is not so abundant in 

 Upper Burlington as in the Lower division ; and may extend 

 into the Keokuk. 



Spirifera forbesi NORWOOD & PRATTEN. 

 Plate xl, fig. 3. 



Spirifer forbesi Norwood & Pratten, 1854: Jour. Acad. Sci., Phila., vol. 



Ill, p. 73. 

 Spirifer forbesi Hall, 1858 : Geology Iowa, vol I, p. 600,pl. xiii, fig 1. 



Shell with hinge-line greatly extended, flattened, mesial fold 

 and sinus small ; radiating ribs, flattened, rather large. 



Horizon and localities. Lower Carboniferous, Burlington 

 limestone : Hannibal, Louisiana, Sedalia, Springfield. 



Spirifera imbrex HALL. 

 Spirifer imbrex Hall, 1858 : Geology Iowa, vol. I, p. 601, pi. xiii, fig. 2. 



Shell similar to 8. forbesi, but hinge-line much shorter, 

 mesial fold much broader, and lines of growth imbricated. 



Horizon and localities. Lower Carboniferous, Burlington 

 limestone : Hannibal, Louisiana. 



Spirifera lineatoides SWALLOW. 



Plate xl, fig. 6. 



Spirifer linealoides Swallow, 1860: Trans. St. Loui3 Acad. Sci. , vol. I. p. 

 645. 



Shell large, robust, transversely elliptical. Ventral valve 

 more convex toward the beak; hinge-line short, rather high; 

 beak strongly incurved. Dorsal valve moderately convex, 

 mesial fold broad, low, or scarcely defined. Surface marked 

 by broad punctato-concentric bands. 



