602 Contributions to Invertebrate Palaeontology. 



simply in close contact with the medio-dorsal portion of the next within, and 

 exposing nearly the entire dorso-ventral diameter of the shell. Volutions 

 transversely subpentangular, being angularly convex on the hack, strongly 

 subangular on the sides, and concave on the abrupt umbilical slope, which 

 forms a somewhat sigmoidal curve resembling an ogee moulding, while the 

 slightly concave ventral surface is quite narrow, and forms a fifth surface. 

 Lateral angles obtuse or round subangular, 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 obsolete 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 strise. Septa and other internal 

 features unknown. 



The shell resembles somewhat N. spectabilis M. and W., but has 

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

 concavity of the umbilical slope and the subangular back are strong 

 distinguishing features. 



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

 Summit Co., Ohio. Cabinet of the School of Mines, N. Y. Cit}-. 



IVaiitiliis (GyrocerasI) siiliqiiadraiigularis. 



Plate XV, fig. 16. 



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

 p. 232. 



Shell of abotit a medium size, consisting of two volutions, as seen on the 

 specimen used, which increase somewhat rai)idly in size with increased length, 

 and are closely coiled so as to bring them in close contact, but not to be in any 

 degree embracing. The inner volution, howeVer, is coiled in so large a circle 

 that it leaves an ojDening 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 particu- 

 larly so. The inner part of the shell has a line of strong node-like undula- 

 tions on each dorsal angle, which become obsolete at about the first third of 

 the second volution. Margin of the aperture greatly extended 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 show- 

 ing about three chambers in the space of one inch, and gradually decreasing 

 in distance toward the earlier part of the shell. On the quadrangular parts, 

 they are deeply receding on the sides and back, and correspondingly advanced 

 on the angles ; a consequence of the quadrangular form on a deeply concave 

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

 Siphon unknown. 



