594 Contributions to Invertebrate Falaeontology. 



CEPHALOPODA. 



Genus IVAUTILUS Breynius. 



IVaiitiliis (Teiuiioclieilus) spectabilis. 



Plate XIV, fig. 22. 



Nautilus spectabilis M. and W., Proc. A. N. S. Pliila., 1860, p. 4G9. 

 N. (Endolohiis) spectabilis Geol. Rept. 111., vol. ii, p. 308, pi. 2f), fig. 1. 



Shell of medium to large size, composed of several volutions, wliich 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-ven- 

 tral 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 and deep, exposing each of the 

 inner volutions to just 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 volu- 

 tion. 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 Worthon 

 (Geol. 111., vol. ii, plate 2.5, fin-. 1), and varies sli<i-htly in having 

 the larger l)ulk 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. Beyond this slight dill'cr- 

 ence they appear to agree as far as the characters are preserved. T]\r 

 difference l)etween this species and Naxtilus Forbesnnus McChes. 

 (Xew Pal. Foss., page G3, and accompanying plate 3, fig. 4 a and b), 



