470 PROCEEDINGS OF THE ACADEMY OF 



discoidal; umbilicus very wide, shallow, and showing nearly all of each 

 inner whorl; volutions about four, increasing gradually in size, slightly 

 embracing, nearly rounded in young shells, but becoming somewhat compressed 

 on the sides and dorsum, in mature individuals having a row of obscure nodes 

 around each dorso-lateral margin; aperture a little oval, its longer diameter 

 being in the direction of the plane of the shell: septa deeply concave, arching 

 gently backwards on the sides and dorsum, and separated by spaces less than 

 one-third the transverse diameter of the whorls; siphuncle small and central; 

 surface apparently smooth. 



Length 3-60 inches; height 3-21 inches; breadth 0-92 inch. 



Locality and position. Alpine, Iowa. Coal Measures. 



Nautilus (Discus) trisulcatus. Shell discoidal, under medium size; 

 umbilicus wide, moderately deep, and showing nearly all of each inner whorl ; 

 volutions slender, increasing very gradually in size, a little broader transversely 

 than the diameter from the dorsum to the ventral margin, ventricose and 

 rounded on each side, and provided with a deep rounded sulcus in each 

 dorso-lateral region. Between these two sulci, the dorsum is narrow, prominent 

 and less deeply grooved, the sulcus being bounded on either side by an angle. 

 Surface retaining traces of rather strong longitudinal lines. Septa deeply 

 concave, and arching distinctly backwards in each of the dorsal depressions, 

 separated on the dorsum by spaces generally less than one-third the transverse 

 diameter of the outer whorl at the place of measurement; siphuncle rather 

 small, and placed a little nearer the dorsal than the ventral side. Length (of 

 a specimen retaining a portion of the nonseptate whorl) 2-33 inches; height 

 182 inches; breadth about 0-87 inch. 



Locality and position. Rockford, Indiana, in beds containing Carboniferous 

 species of Goniatites, but usually regarded as Upper Devonian. 



Nautilus (Discus) digonus. Shell rather small, subdiscoidal; umbilicus 

 comparatively large, moderately deep, and showing all of each inner whorl ; 

 volutions about three or four, in contact, but not embracing, increasing 

 gradually in size, broad and nearly flat on the dorsal side, which is marked 

 by two very obscure longitudinal depressions near the aperture; distinctly 

 angular on each dorso-lateral margin, thence rounding regularly into the 

 umbilicus; surface of cast retaining traces of regular, equidistant longitudinal 

 lines, and much finer and more closely arranged transverse stria?; aperture and 

 section of the whorls nearly semicircular, the outer or dorsal side being almost 

 straight, and the inner rounded. Septa distinctly concave; their margins 

 curving obliquely backwards on the sides of the whorls, from the dorso-lateral 

 angles, and deflected backwards in crossing the dorsum. Siphuncle small, 

 located about one-third the diameter of each septum from the dorsal side. 



Length, (of an imperfect specimen, about one-third of the outer whorl of 

 which is non-septate,) 1-20 inch; height 1 inch; breadth across the dorsum 

 of the outer whorl near the aperture, 0-62 inch; diameter of same from the 

 dorsal to the ventral side, 0-40 inch. 



Locality and position. Same as last. 



Nautilus (Discus) Sangamoneksis. Of this species we have seen but a 

 single specimen consisting of about half of one volution. It is a little wider 

 transversely than deep, and increases gradually in size from the smaller to the 

 larger end, being evidently part of a discoidal shell, with an umbilicus 

 about equalling the transverse diameter of the outer whorl. On the dorsum 

 , it is nearly flat, or but slightly convex, and the sides are a little concave. The 

 ventro-lateral regions are obliquely flattened, so as to form an abrupt slope 

 into the umbilicus, leaving a subangular prominence between the umbilicus 

 and each slightly concave side. The ventrum is moderately concave along the 

 middle, for the reception of the inner whorls, each of which was probably 

 about one-third hidden. 



[Oct. 



