PALEONTOLOGY. 487 



and ornamented by a series of nodes which are strong and very distinct on the 

 inner coil, broad and rounded on the first part of the last volution, and become ob- 

 solete on the outer third. The substance of the shell has been very thick and 

 strong, and the surface shows no evidence of growth-markings or striae. Septa 

 and other internal features unknown. 



The shell resembles somewhat A 7 ". spectab : lis M. and W., but has a 

 smaller number of coils in a shell of corresponding size, while the con- 

 cavity of the umbilical slope and the subangular back are strong dis- 

 tinguishing features. 



Formation and Locality. — In the Coal Measures at Springfield, Sum- 

 mit county, Ohio. Cabinet of the School of Mines, N. Y. City. 



Nautilus {Gyroceras?) subquadr angular is. 

 Plate XI, fig. 16. 

 Xautilus (Gyroceras?) subquadrangularis Whitf., Ann. N. Y. Acad. Sci., 1882, p. 

 232. 



Shell of about medium size, consisting of two volutions, as seen on the spec- 

 imen used, which increase somewhat rapidly in size with increased length, and are 

 closely coiled so as to bring them in close contact, but not to be in any degree em- 

 bracing. The inner volution, however, is coiled in so large a circle that it leaves 

 an opening within it of about one inch in diameter. The shell is at first circular in 

 section, but before the completion of the first coil the form has become modified so 

 as to produce a subquadrangular section, narrowest on the dorsal side, and the 

 second volution becomes distinctly quadrangular, being nearly as wide on the 

 dorsum as across the lateral face ; but the angles are all distinctly rounded, and the 

 inner or umbilical margins most particularly so. The inner part of the shell has a 

 line of strong node-like undulations on each dorsal angle, which becomes obsolete 

 at about the first third of the second volution. Margin of the aperture greatly ex- 

 tended on the sides beyond the line of the inner edge, and apparently sinuate on 

 the back. Septa deeply concave and numerous ; those at the base of the outer 

 chamber showing about three chambers in the space of one inch, and gradually de- 

 creasing in distance toward the earlier part of the shell. On the quadrangular 

 parts, they are deeply receding on the sides and back, and correspondingly ad- 

 vanced on the angles ; a consequence of the quadrangular form on & deeply con- 

 cave septum. Surface of the shell apparently smooth and the substance thin. 

 Siphon unknown. 



The species is peculiar in its quadrangular form, and in the wide 

 opening through the centre : in these characters it differs from any pre- 

 viously described species. It is of a form that is with difficulty placed 

 in the genus Nautilus — -its characters, so far as the external features are 

 concerned, nearly resembling those of Gyroceras — and in the absence of 

 a knowledge of the position of the siphuncle, must remain doubtful. 



Formation and Locality. — In limestone of the Coal Measures, at Can- 

 field, Ohio. Collected by H. C. Bowman, and now in the cabinet of the 

 School of Mines, New York City. 



The following species are forms which characterize two different beds 

 of chert in the Coal Measures in the Hocking Valley, and are sufficiently 

 pronounced to leave no doubt of their true horizon. These beds have 

 been used as horizons from which to determine the position of the rocks 

 in that vicinity. 



