FOSSILS Otf THE SILURIAN AND DEVONIAN ROCKS. 187 



Genus Cyclonema, Han. 



Cyclonema, Hall. Pal. K Y., Vol. 21852. 

 Etymology: kuklos, a circle; nema, a thread. 



Shells turbinate, thin; spire short, consisting of few volutions, which in- 

 crease rapidly from the apex ; aperture large, rounded anteriorly, and some- 

 what flattened on the columella side ; umbilicus none ; surface strongly 

 marked by spiral, thread-like striae, which are cancellated by finer striae. 



This genus includes shells which have been referred to Pleurotomaria, Litto- 

 rina and others, but which have no slit or indentation in the outer lip or a 

 band upon the volutions. 



The surface is marked by elevated striae parallel to the direction of the 

 volutions, and the spaces between these are marked by finer striae crossing the 

 others obliquely ; tliese latter, however, are often obsolete. 



The Pleurotomaria bilix of Conrad is the type of this genus. 



Cyclonema cancellata. HALL. 



Plate XX., figures 10 and 11. 



Littorina cancellata, Hall. Geol. Kep. 4th Dist. N. Y. 1843. 

 Cyclonema cancellata, Hall. Pal. N. Y., Vol. 2, page 90 1852. 



Obtusely sub-conical or globose, with a short spire ; volutions about four, 

 rounded, rapidly increasing from the apex, so that the last one occupies 

 almost the whole bulk of the shell ; aperture scarcely expanded. 



Surface marked by prominent thread-like lines, coincident with the spire, 

 which are decussated by finer elevated striae in a slightly oblique direction. 



The size of this shell varies greatly, from one measuring only a few lines to 

 the size shown in the illustrations. In .young individuals, the decussating 

 striae are usually well preserved, while they gradually become obsolete in older 

 specimens, which are also often distorted by pressure. 



Formation and Locality. Occurs in the lower strata of the Niagara group in the quarries east of 

 the city of Louisville, where, however, it is a very rare shell. The specimen from which this description, 

 and the figures 10 and 11, on plate 20, were made, belonged to the collection of the late Dr. James Knapp; 

 no others are known to me. 



Gyclonema rugaelineata. HALL AND WHITFIBLD. 



Plate XXXIII., figure 21. 



Euomphalus (Cyclonema) rugaelineata, H. and W. 24th Rep. on N. Y. State Cabinet, p. 1861872. 

 Euomphulus (Cyclonema) rugaelineata, H. and W. 27th Rep. on N. Y. State Cabinet, pi. 13 1875. 



Shell of medium size, depressed turbinate, with four or five volutions, which 

 increase very rapidly ; they are rounded, very convex, and the last one is very 



