FOSSILS OF THE COAL MEASURES. 591 



slope of the spire, or hut slightly convex; lower ones some- 

 times a little projecting' at their lower margins immediately 

 above the suture: last one distinctly angular around the 

 middle, and hut moderately produced below the angle, 

 where it is a little convex. Umbilical region not indented. 

 Suture generally well defined between the lower whorls, 

 and merely linear above. Aperture rhoinbic-subquadrate. 

 Surface showing, under a magnifier, small, very slightly 

 oblique lines of growth, which are sometimes crossed on 

 the middle of the flattened outer slope of the body whorl by 

 very faint traces of two revolving ridges, and below the an- 

 gle, on the under side, by traces of another revolving ridge. 

 Length, 0.70 inch ; breadth, 0.30 inch; apical angle a lit- 

 tle convex on its slopes, divergence about 30 deg. 



This species will be readily distinguished from our 0. Salteri, the 

 typical species of the genus, from the same locality and position, by its 

 larger size, smaller number of whorls, greater apical angle, and par- 

 ticularly by never having the two linear revolving ridges just below 

 the suture, so characteristic of that species. As mentioned in the de- 

 scription, it sometimes, though rarely, shows traces of two very obscure 

 revolving ridges on the flattened part of the body whorl, but these are 

 midway between its principal angle and the suture, while those on 0. 

 Snlttri are always very distinct, and placed just below the suture. The 

 principal angle on the body whorl of 0. Sttlteri is also much more 

 strongly defined, being a true carina. 



From the several species of Po1yphf'in<ni*i* of our Coal Measures, such 

 as our P. iimrnata. P. peracuta. etc.. which it somewhat resembles, this 

 species will be distinguished by its angular body whorl, and particu- 

 larly by not having this whorl produced below, and its columella curved 

 and truncated, so as to produce the peculiar effuse character at the 

 base of the aperture seen in that genus. 



Locality and position Hodge's creek, Macoupin x'ounty, Illinois. 

 Lower part of Coal Measures. 



