FOSSILS OF Till; COAL MEASURES. (jll 



in- rather gradually in sixe. very slightly compressed on 

 the dorsal and lateral surfaces, but without the compres- 

 >imi imparting any angularity to the dorso-lateral and ven- 

 tral margins, which are rounded: each turn concave within 

 for the reception of the inner volutions. Septa nioderately 

 coneave. separated by >paces measuring on the outer side 

 1 38 than one-third the dorso-ventral diameter of the whorls 

 at the point of measurement, all crossing the lateral and 

 outer sides of the volutions with a broad bark ward curve. 

 Siphon scarcely more than its own breadth from the inner 

 margin. Aperture, judging from the section of the whorls, 

 about as wide transversely as its dorso-ventral diameter, 

 sub-quadrilateral, approaching sub-reniforui, in conse- 

 quence of the sinuosity of the inner side. (Surface un- 

 known.) 



(Greatest diameter, about 4.70 inches; convexity, about 

 12.75 inches: breadth of umbilicus, 1.45 incln >. 



Tliis species (lifters from all of the others resembling it in other 

 respects, known to us. from our rocks, in having its volutions without 

 any traces of m. 



lity <</j/7 puxitioH Upper Coal Measures; La Salle, Illinois. 



(inMATITKS ( "n.M I'ACTUS. M. aild AY. 



PI. 31. Fi_'. -i. 

 fita compact**, MEEK and WOBTHES, 1865. Proceed. Acad. Xat. Sci.. Phila., p. 154. 



SHELL subdiscoidal : umbilicus wide, or about twice the 

 dorso-ventral diameter of the last turn near the aperture, 

 moderately deep, and showing about half of each inner 

 turn. Volutions four, nearly twice as wide as the diame- 

 ter in the direction of the plane of the shell, broadly 

 rounded externally, and each provided with a broad mode- 

 rately deep concavity on the inner side for the reception 

 of the next whorl within: sides rather narrowly rounded 

 near the umbilicus, and rounding off more gradually to 

 the periphery, the most prominent part being within the 



