Impressions of Carboniferous and Jurassic Nautiloids. 223 



polygonalis (B.M. no. o. 2847) from the Inferior Oolite; the 

 locality is not recorded. It is a longitudinal section of a shell 

 and shows the course of the anterior boundary (a) of the 

 muscular impression from the umbilicus to the periphery. 

 Not only does this muscular impression greatly resemble that 

 of the recent Nautilus (iV. pompilius), but the curvatures of 

 the sutures are also nearly identical, as may be seen by com- 

 paring them with those of fig. 1. 



Nautilus obesus?, J. Sowerby *. 



The only example of this species known to us which 

 shows any trace of the muscular impression is a cast of a large, 

 crushed, and much broken body-chamber from the Iron- 

 stone (Inferior Oolite) of Duston, Northamptonshire (B.M. 

 no. 82328 b). This measures 14 inches along the curve 

 of the periphery, the last-formed septum being 4| inches 

 wide, and the width of the aperture 9k inches. Fig. 5 has 



Fisr. 5. 



been reduced with the camera from a tracing of the actual im- 

 pression : a indicates the anterior and p the posterior boundary ; 

 s indicates a portion of the last-formed septum. The irregular 

 line on either side of the figure represents merely the broken 

 edge of the umbilicus. Although the specimen is so badly 

 preserved, not only can the anterior boundary of the muscular 

 impressions and annulus be made out, but a portion also of 

 the posterior boundary. On one side of the body-chamber 

 several lines close to and concentric with the anterior boun- 

 dary of the impression indicate former points of attachment 

 of the anterior edge of the shell-muscle, and may be compared 

 with similar lines to be observed in the shell of the recent 

 Nautilus f. 



Nautilus clausus, d'Orbigny \. 



Fig. 6 was traced from a young specimen (2 inches in 



* Ibid. vol. ii. 1810, p. 51, pi. exxiv. 



t See Geol. Mag. dec. iii. vol. vi. p. 495 (Nov. 1889), fig. E. 

 | ' Puleontologie Francaise, Terr. Jurassiques,' torn. i. 1842, p. 158, 

 pL xxxiii. 



