Contributions to Invertebrate Palaeontology. 591 



similar to that of many others, but the peculiar zig-zag feature of 

 the ornamenting ridges will at once distinguish it from all other 

 described species. Several ornamented forms of the genus are 

 known from the Coal Measures, but their markings consist of 

 nodes, either promiscuously scattered or arranged in patterns. 



Formation and Locality. — In the limestone of the age of the St. 

 Louis and Chester beds of Illinois (Maxville limestone), at New- 

 tonville, Ohio. 



Genus HOLOPEA Hall. 



Holopea Ne\%tonensis. 



Plate XIV, fig. 12. 



Holopea Newtonensis Whitf., Ann. N. Y. Acad. Sci., 1882, p. 224. 



Shell of medium size, ovate in outline and ventricose, with a moderately 

 elevated spire and extremely ventricose volutions, which increase very rapidly 

 in bulk from the apex. Volutions three and a half to four in number, with 

 strongly rounded surfaces and moderate sutures. Apical angle about seventy 

 degrees. Aperture broad ovate, modified on the inner side by the preceding 

 volution, pointed at the upper end and broadly rounded at the base. Surface 

 of the shell smooth and the substance very thin. 



The form of the shell is much like that of a 3Iacrochilus, but the 

 substance is much thinner than those usually are, and the base of 

 the columella is not prolonged, nor is there a solid axis; but speci- 

 mens show satisfactory evidence of having been distinctly and 

 largely umbilicated. 



Formation and Locality. — In the Maxville limestone (Chester), 

 at Newtonville, Ohio. Collection of Columbia College, New York. 



Genus MACROCHEILUS Phillips. 



Maci'oclieilus siibcorptileiitus. 



Plate XIV, fig. 14. 



Afacrocheilus suhcorpulentus Whitf., Ann. N. Y. Acad. Sci., 1882, p. 224. 



Shell small, the specimens observed not exceeding five-eighths of an inch in 

 length, and the diameter rather exceeding half the length ; spire conical, the 

 apical angle being about fifty degrees. Volutions about three or tliree and a 

 half, rapidly increasing in diameter and very ventricose, the last one forming 

 more than half the length and much the greater bulk of the shell ; suture 

 deep and well marked. Aperture ovate, short, and oblique. Surface of the 

 shell smooth'. Columella not seen. 



