CEPHALOPODA— ORTHOCHOANITES. 85 



nummuloidal, slightly excentric. Sutures with broad ventral sad- 

 dles in adolescent and usually with slight, ventral lobes in adult. 

 Living chamber from one fourth to one half volution.. Surface 

 with revolving ridges, or striae, often smooth in adult. Devonic. 



96. N. bucinum (Hall). (Fig. 1303.) Devonic. 



Comparatively small; volutions rapidly enlarging, contiguous, 

 but not embracing; section broadly elliptical; siphuncle near con- 

 cave dorsal side; surface with regular, sharply elevated spirals, 

 about four in 10 mm. near aperture, with finer spirals between. 



Fig. 1303. Nephriticeras bucmum, X /^ > ^^^ middle figure shows part of shell 

 remaining. (After Hall, Pal. N. Y., V. ) 



Agoniatite limestone and Hamilton of New York; Hamilton of 

 Maryland. 



97. N. liratum (Hall). Devonic. 

 Similar to preceding, but volutions rapidly enlarging, barely con- 

 tiguous, siphuncle centren or subcentren, and spirals coarse, 

 rib-like. 



Goniatite limestone (Marcellus) of New York; Lower Hamilton 

 of Pike County, Pennsylvania. 



98. N. magister (Hall). (Fig. 1304.) Devonic. 

 Large; whorls subglobose, embracing to one third the diameter 



of the preceding volution, rapidly expanding; section of whorls 

 elliptical, with broad, rounded sinus ; siphuncle large, expanding 

 abruptly and becoming cylindrical between septa; surface with 

 lamellose growth lines and wide, obscure, radiating lines. 

 Hamilton of New York. 



99. N. maximum (Hall). Devonic. 

 Large; differs from the preceding in the more circular, trans- 

 verse section of the whorls, and less coiled volutions; siphuncle 



