426 
PALAEONTOLOGY OF NEW YORK. 
Septa regular and slightly advancing from the centre of the dorsum to the 
umbilical angle; thence curving backward, and again forward, they are 
recurved from the ventro-lateral angle, making a gentle inflexion across the 
lateral face of the volution, and a more abrupt, retral curve on the ventral 
face. This direction of the septa corresponds very nearly with their direc¬ 
tion in the simpler forms of Goniatites, presenting a low saddle on the 
ventro-lateral and dorso-lateral angles, and a broad, shallow lateral, and nar¬ 
rower ventral lobe. Convexity of the septa, measured across the dorso- 
ventral diameter, 112°. Siphuncle small, near the convex ventral side; its 
elements not fully known. 
Test and surface-markings unknown. 
The specimen described is an internal cast, measuring across the disc 
230 mm.; the dorso-ventral diameter of the outer volution at the base of the 
air-chamber is sixty-five mm. 
This species bears considerable general resemblance to N. ( Discites ) Marcel- 
lensis, but is distinguished by its larger size, re-entrant volutions, form of the 
transverse section, more gradually enlarging tube, and less expansion of the 
grand chamber. 
Formation and locality. The specimen was found in a loose mass of limestone 
of the Upper Helderberg group (the original source of which is unknown), at 
Ann Arbor, Michigan. 
Nautilus (Discites) inopinatus, n. sp. 
PLATE CX, FIGS. 1, 2. 
Shell discoid* the greatest thickness of the disc being a little less than half the 
greatest transverse diameter. Volutions three or four, contiguous; some¬ 
what gradually expanding in the inner volutions, and much more rapidly in 
the outer one. Umbilicus wide, showing the entire lateral faces of the 
volutions. Transverse section quadrangular, trapezoidal, the base shorter 
than the sides; sides nearly straight, and gradually diverging from the base; 
peripheral margin curved, convex outwardly, and longer than the side. Tube 
