NATURAL SCIENCES OF PHILADELPHIA. 469 



of a septate specimen, incomplete at both ends, 1-18 inches; breadth of smaller 

 end 1 inch, do. of larger end 2-97 inches. 



Locilily and position. Near Springfield, Illinois. Upper Coal Measures. 



Genus NAUTILUS, Breynius. 



Nautilus subglobosus. Shell under medium size, subglobose, broadly rounded 

 over the dorsum and sides; umbilicus (in casts) rather small, deep, conical, 

 or with nearly vertical sides, showing rather less than the half of each inner 

 whorl; volutions about three, increasing rapidly in size, especially in breadth, 

 deeply embracing, subangular on the sides around the umbilicus; septa rather 

 deeply concave, arching very slightly forward over the dorsal region, where 

 they are separated by spaces a little less than one-fifth their own greater 

 (transverse) diameter; aperture transversely sublunate, or subreniform; lip 

 deeply sinuous on the dorsal side; siphuncle central; surface apparently 

 smooth. Length 2-11 inches; height 1-72 inch; breadth at aperture 1-95 inch. 

 This species is related to the following, but differs in having a wider umbilicus, 

 with more rapidly expanding whorls. It is also more broadly rounded on the 

 dorsum, and its septa are rather more closely arranged in proportion to the 

 breadth of the whorls. 



Locality and position. Chester, Illinois. Chester Limestone of Lower Car- 

 boniferous series. 



Nautilus Chesterensis. Shell under medium size, subglobose, rounded 

 over the dorsum and sides; umbilicus (in casts) small and deep, with nearly 

 vertical walls, probably almost closed in adult specimens retaining the shell, 

 apparently showing little of the inner whorls ; volutions about three ; increasing 

 moderately in size, rather deeply embracing, abruptly rounded, or subangular 

 around the umbilicus; septa not very concave, arching very slightly forward 

 over the dorsal region, where they are separated by spaces a little less than 

 one-fourth their own transverse diameter; siphuncle very nearly or quite 

 central; aperture (as inferred from a section of the whorls) transversely 

 subreniform; (surface unknown). Length 2-43 inches; heighth about 1-88 

 inches; breadth near the aperture about 1-80 inch ; breadth of umbilicus (in 

 cast) 0-54 inch. 



Locality and position. Same as last. 



Nautilus spectabilis. Shell large, subglobose; umbilicus moderately wide, 

 deep, subcorneal, and showing rather more than half of each inner whorl ; 

 volutions increasing rather rapidly in size, or more than doubling their diameter 

 each turn, broadly rounded over the dorsum, moderately concave within, and 

 very narrowly rounded, or subangular along the middle of each side, where 

 they are ornamented by a series of low nodes, some fourteen to sixteen of which 

 maybe counted on either side of each turn; section of the whorls subelliptical, 

 the breadth being rather more than double the diameter from the dorsal to the 

 umbilical side; siphuncle located a little outside of the centre. Septa distinctly 

 concave, arching slightly forward over the dorsum, where they are separated 

 by spaces less than one-fourth their own transverse diameter. (Surface, 

 aperture, and number of whorls unknown.) 



Length of a specimen, consisting entirely of septate whorls, 4-50 inches; 

 height of do. 3-47 inches; breadth of the aperture 3-20 inches. 



Locality and position. Gravel Creek, Randolph County, Illinois. Chester 

 Limestone, of Lower Carboniferous series. 



Nautilus (Discus*) planorbiformis. Shell of medium size, compressed 



*We retain Prof. King's name Discus, in a subgeneric sense, for all thediscoidal forms 

 with a central siphuncle, simple septa, and slender contiguous whorls, all exposed in a 

 wide, shallow umbilicus. It seems not to be quite synonymous with Disciles, of McCoy, 

 which is described as having the siphuncle " near the outer edge of the periphery." 

 We have some doubts whether such forms should be retained in the same genus with 

 the living species of Nautilus. 



I860.] 



