INVERTEBRATES. 305 



are not more widely separated than near the smaller end. 

 Traces of fine transverse stride are also seen on well preserved 

 specimens, both between -and upon the costse. (Septa and 

 siphuncle unknown.) The largest specimen we have seen is 

 about five inches in length (both extremities being incomplete), 

 and 1.83 inches in its greater diameter at the larger end, while 

 its greater diameter at the smaller end is near 0.70 inch. 



This species bears some resemblance to O. dactyliophorum, de Koninck 

 {Ann. Foss. Ter. Carb. Belg., p. 518, pi. xlvii, fig. 1, et xlviii, fig 7 a, 7 b), 

 but differs in being more tapering, and somewhat compressed instead of round. 

 It is also more tapering than 0. annidatum, of Sowerby. Prof. Swallow has 

 described, from the same horizon as this, a similar species under the name 0. 

 chesterensis (Trans. St. Louis Acad. Sci., vol. ii, p. 98, 1862), but our shell 

 differs in having fewer and more distant costae, there being generally about 

 four of them in a space equaling the transverse diameter, while 0. chesterensis 

 has eight in the same space. 



Locality and position : Same as preceding. 



Genus NAUTILUS, Linnseus, 1758. 



(Syst. Nat. Ed., 10, t. i, p. 109.) 



Nautilus globatus, Sowerby? 



PI. 24, fig. 5 a, 5 6. 



Nautilus flobatus, Sowerby, 1825. Min. Conch., v, pi. 481, fig. 1 and 2. 

 Nautilus Wrightii, Fleming, 1828. Brit. Anim., p. 230. 



Nautilus bistrialis, Phillips, 1836. Geol. Yorksh., 11, p. 232, pi. 17, fig. 20 and 28. 

 Nautilus subtjlobosics, Meek and Worthen, Oct., 1860. Preceed. Acad. Nat. Sci., 

 Philad., p. 469. 



Shell rather under medium size, subglobose, broadly round- 

 ed over the dorsum; umbilicus (in internal casts) rather small, 

 deep, and conical, or with nearly vertical sides; volutions about 

 three, increasing rapidly in size, particularly in breadth, deep- 

 ly embracing, subangular around the margins of the umbilicus 

 on each side; outer chamber forming about half of one volu- 



39 Sept. 19, 1SC6. 



