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 stria?, which, 

 on some parts, are wider than the intermediate spaces. The inner lamina? 

 of the shell are marked by very fine, revolving stria?, 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. 



