520 PALSONTOLOOT OF ILLINOIS. 



but without distinct, regular sinuosities, excepting some- 

 times obscure ones around the front. Surface more or less 

 roughened by undulating striae, and strongly defined ridges 

 of growth, with sometimes obscure traces of a few radia- 

 ting costae near the anterior margin.* 



Hight to summit of apex, 0.96 inch ; antero-posterior 

 diameter, 1.63 inches; transverse do., 1.50 inches; (these 

 latter being also the dimensions of the aperture.) 



We have intentionally omitted to mention, in the description, the 

 opening near the apex of this shell, mentioned by Prof. HALL, because, 

 with the original typical specimen now before us, we feel quite confi- 

 dent that the opening described by Prof. HALL is an accidental break 

 in the shell, and not a natural perforation. 



The reasons for this conclusion are: first, the appearance of the open- 

 ing itself; second, the fact that it does not exist in other specimens 

 agreeing in their specific characters, from the same locality and position; 

 and third, the fact that it is against all analogy for a shell of this genus 

 or family to have a natural perforation at the apex, such as we see in 

 the Fissurellidce. 



Locality and position Warsaw, and Nauvoo, Illinois ; from the Keo- 

 kuk division of the Lower Carboniferous series. 



PTEROPODA. 

 GENUS, CO1SUL ARIA. 



CONULARIA SUBCARBONARIA, M. and W. 



PI. 19, Fig. 4. 



ConularM carbonaria, MEEK and WORTHED, 1865. Proceed. Acad. Nat. Sci., Phila., p. 253. 

 Comp. O. Yerneuttii, Enimons, 18 . Manual Geol., See. Ed., p. 159, fig. 7. 



SHELL attaining a large size, very thin, more or less 

 distinctly and nearly equally four-sided, the sides and an- 

 gles being somewhat rounded, and converging towards the 

 smaller extremity, at an angle of about 18 c ; section quad- 

 rangular mesial furrow of each side very obscure, those at 



* Some of the specimens show some indications of very fine, crowded, radiating strise, but these 

 appear rather as if caused by the pressure arid slipping of the matrix. 



