542 PALEONTOLOGY OF ILLINOIS. 



gins diverging towards the aperture at an angle of about 

 eighteen degrees, while those of the narrower sides diverge 

 at an angle of about twelve or fifteen degrees ; transverse 

 section (in a distorted specimen) rhombic; angles at the 

 four corners rather deeply furrowed; sides without a dis- 

 tinct mesial furrow. Surface marked by comparatively 

 strong, rather prominent, apparently smooth, sharp, trans- 

 verse costsB, about half as wide as the rounded furrows 

 between; in passing across the sides these curve more or 

 less upwards toward the aperture, and are often interrupted 

 and alternating in the middle; costse and spaces between, 

 so far as can be seen, without crenulations. 



Length of a specimen incomplete at both extremities, 

 6.10 inches; breadth of one of the wider sides at smaller 

 end, 0.52 inch; do. of same at larger end, 1.88 inches; 

 breadth of narrow sides at smaller end, about 0.50 inch; 

 do. of same at larger end, about 1.30 inches. 



From a comparison with a tracing made from Prof. SWALLOW'S type 

 of his C. Missouriemis, we are led to regard this as his species, though 

 as his specimen is rather imperfect, it is possible some specific differ- 

 ences might be observable, if we could compare good specimens. The 

 rhombic form in both examples is doubtless due to oblique pressure, 

 which has probably imparted the cariuated character to the acute 

 lateral edges mentioned by Prof. SWALLOW. 



The species is most remarkable for its coarse, rather distant, and 

 apparently smooth transverse costae and large size. 



Locality and position Prof. SWALLOW'S typical specimen was obtain- 

 ed from some of the ( upper f ) members of Lower Carboniferous Lime- 

 stones of Cooper county, Missouri. The specimen from which our 

 figures and description were prepared was found in the Warsaw 

 division of the Lower Carboniferous Limestone series, at Warsaw, 

 Illinois. 



