INVERTEBRATE FOSSILS OF THE ST. LOUIS GROUP. 



PROTOZOA. 

 SPONGIJE. 



PETROSPONGIA. 



Genus SPHENOPOTERIUM, M. and W. (See page 145.) 



Sphenopoterium cuneatum, M. and W. 



PI. 19, fig. la, lb, lcand Id. 



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

 Philad., p. 448. 



Compressed, cuneate, longer than wide ; base sharp, a little 

 rounded at the lateral edges. Cells from two or three to about 

 five, rather distant, deep, conical, or a little compressed below, 

 and arranged alternately on each lateral edge; rounded or 

 slightly oval at the aperture, and directed obliquely outwards 

 and upwards ; often having one or two slightly prominent 

 ridges extending part of the way up the inside; perforations of 

 the walls numerous and distinct. Surface strise fine, closely 

 arranged, rather regularly and minutely crenulated ; directed 

 obliquely inwards and downwards from the apertures of the 

 cells, and passing more or less nearly parallel to each other, to 

 the base, on the lower flattened portion. Length, 0.75 inch; 

 breadth, 0.50 inch ; thickness, 0.22 inch. 



