INVERTEBRATE FOSSILS OF THE KEOKUK GROUP. 



PROTOZOA. 

 SPONGIJE. 



PETROSPONQIA. 



Genus SPHENOPOTERIUM, M. and W., 1860. (See p. 145.) 



Sphenopoterium obtusum, M. and W. 



PI. 17, Pig. 2 a, 2 6, 2c, 2d (by error a on the pi.), 2e. 



Sphenopoterium obtusum, Meek and Worthen, Oct., 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 448. 



Short, abruptly cuneate below, wider than high; basal 

 edge slightly sinuous in the middle ; flattened sides, expanding 

 rapidly upwards from the obtuse basal carina. Cells from four 

 to about nine, comparatively large, and of moderate depth, 

 conical, and where not more than four or five, rounded and 

 separated by thick interstices, but becoming angular, with 

 thinner intervening partitions, where more crowded. Surface 

 strise fine, irregular, and showing a tendency to converge 

 towards the middle of the base, anastomosing in such a manner 

 as to form a kind of shagreen-like style of ornament. Length 

 or height of a large individual containing nine cells, 1 inch ; 

 breadth of same, 0.98 inch; thickness, 0.66 inch. 



Locality and position: Nauvoo, Illinois; Keokuk division ef the Subcarbonif- 

 erous series. 



30 Sept. 8, 1866. 



