480 GEOLOGY OF OHIO. 



CEPHALOPODA. 



Genus NAUTILUS Breynius. 

 Nautilus ( Temnocheilus) spectabilis. 

 Plate X, fig. 22. 

 Nautilus spectabilis M. and W., Proc. A. N. S. Phila., 1860. p. 469. 

 N. (Endolobus) speetbbilis Geol. Rept., 111., vol. ii, p. 308, pi. 25, fig. 1. 



Shell of medium to large size, composed of several volutions, which increase 

 rapidly in size, and are transversely elliptical in a transverse section ; the diameter 

 from side to side being about one-third greater than the dorso-ventral diameter at 

 the same point; the lateral edges being obtusely angular, and the dorsal portion 

 of the section larger and more convex than the inner part, strongly convex and 

 subangular on the back. Inner surface of the volution strongly impressed by the 

 one preceding, which it embraces to near the point of greatest diameter. Umbilicus 

 very broad a*nd deep, exposing each of the inner volutions to iust beyond the point 

 of greatest transverse diameter, the umbilical surface of the volutions being 

 moderately convex but quite abrupt. The sides of the volutions are marked by a. 

 series of nodes of considerable strength and size, arranged at regularly increasing 

 distances, and occurring, as nearly as can be determined from the example on hand,, 

 at about every second septum. The nodes are situated on the crest of the side, and 

 are obtusely rounded and prominent. Septa moderately distant and but slightly 

 bent downward on the dorsum. On a specimen measuring about three inches in 

 its greatest diameter, the whole of which is septate, they are arranged at about one- 

 third of an inch apart, near the outer extremity of the last volution. Siphuncle/ 

 not observed, and the depth of the septa not ascertained. The surface of a portion 

 of the specimen bears marks of a series of strong varices of growth, which have 

 crossed the dorsum and show a strong retral sinus or notch in the margin of the lip 

 at this point. The varices are seen on the inner portion of the last volution and 

 appear to have been arranged at distances nearly corresponding to the septa at the 

 same place. No other markings of the surface are retained. 



The specimen from the Maxville limestone is somewhat smaller than 

 that from the Chester limestone figured by Meek and Worthen (Geol. 111., 

 vol. ii, plate 25, fig. 1), and varies slightly in having the larger bulk of 

 the volution outside of the line of nodes that occur on the lateral angles ; 

 or in other words the dorsal portion is larger than the ventral, though on 

 the inner volutions of the specimen this character is not so distinct. Be- 

 yond this slight difference they appear to agree as far as the characters are 

 preserved. The difference between this species and Nautuus Forbesanus 

 McChes. (New Pal. Foss., page 63, and accompanying plate 3, fig. 4 a and 

 b), from the Coal Measures, Mercer county, 111., are almost too slight for 

 specific distinctions, where all the examples are internal casts. In the 

 last-named species the bulk of the volution is on the inner side of the 

 line of nodes instead of on the outside as in the one now under con- 

 sideration, while in the one now figured by M. and W. it is very 

 nearly or quite equally divided. Where all other features are the same in 

 all, these would scarcely seem to be of specific importance. 



From the strong sinus in the lip on the back of the shell the species- 

 has been referred to McCoy's genus Temnocheilus, and would be so 

 classed if that division should be retained. 



Formation and locality.— In. the Maxville limestone (Chester), near 

 Rushville, Ohio, from the collection of Prof. E. B. Andrews. 



