CEPHALOPODA. 
423 
mens indicate a small, shallow depression, close to the dorsal margin, on the 
concave faces of the septa. 
Siphuncle large, expanding abruptly, and becoming cylindrical between the 
septa; diameter about one-fifth the dorso-ventral diameter of the tube at the 
same point; position subcentral, above the middle, or ventral as measured in 
a direct dorso-ventral direction, at right angles to the axis of the shell; and 
below the centre, or dorsal, as measured on the convex face of the septa; 
surrounded by an areola on the septa; section circular. Casts of the interior 
show a narrow, raised band on the ventral side, having a width of 1.5 mm. 
Test partially preserved, having a thickness of 1.5 mm. on the sides of 
the volution, and .75 mm. on the ventral portion. The surface shows 
broad, lamellose lines of growth, and obscure, wide radiating striae, which, 
on some parts, are wider than the intermediate spaces. The inner laminae 
of the shell are marked by very fine, revolving striae, which are scarcely 
elevated, but constitute an intimate part of the shell structure. The tube is 
ornamented with low, rounded, obscure nodes on the dorso-lateral faces, 
which are about as frequent as the septa. These nodes, in some cases at 
least, appear to be connected with a more abrupt advance of this part of the 
shell; and are preserved upon the cast of the interior. 
The internal cast presents no unusual features. Owing to the extremely 
imbricating character of the septa, the thin margins of the chamber fillings 
are usually broken. Measurements taken from a large, nearly entire cham¬ 
ber of habitation, give a length of 190 mm., with a greatest lateral diameter 
of 170 mm., and the greatest dorso-ventral diameter of 140 mm. The diam¬ 
eter of the siphuncle between the septa is seventeen mm., and at the septa 
ten mm. The diameter of the specimen, plate 62 and plate 63, measured 
across the volutions, is 185 mm. 
This species is distinguished by its great size and broad, re-entrant volutions. 
Comparisons with N. maximus have already been made on page 420. 
Formation and locality. In some concretionary calcareous layers, in the upper 
shales of the Hamilton group, on the shore of Lake Erie, in the town of Ham¬ 
burgh, Erie county, N. Y. 
