﻿BEITISH FOSSIL CEPHALOPODA. 211 



^ a whorl at least, and remains in contact with the inner whorls, while the 

 outer curve loses some of its curvature, so that the surface spreads out 

 radially ; it does not at all contract in the perpendicular direction, but, if any- 

 thing, expands. There is a thickening of the shell near the aperture. The 

 septa are fairly convex transversely ; the sutures are much curved forward on 

 the outside. The small inner lobe noticed in recent and several extinct Nautili is 

 well shown. The distance of the septa greatly varies, being from -§- to -^ the 

 diameter of the whorl. The siphuncle lies a little beyond the centre towards the 

 outside, and is of moderate size. In some examples, apparently of this species, no 

 siphuncle can be seen in this position, or indeed in any other ; but elsewhere they 

 are broken down. The supposed external siphuncle of Salter is a shell lodged in 

 the body-chamber. 



Relations. — This appears to be the central figure of the group whenever repre- 

 sentatives of it occur. Perhaps the name Nautilus Biddulphii ought to be adopted ; 

 but Sowerby's description is not sufficient for identification. 



Distribution. — In the Wenlock Beds of Dudley (1) and Malvern (1) ; in the 

 Lower Ludlow of Ledbury (11) and of Ludlow (1). Sowerby's Lituites Biddulphii 

 was from Wenlock Limestone, Ledbury. 



Nautilus Holtianus, Blake, PI. XXVIII. fig. 1. 



Syn. 1865. Lituites Holtianus, Salter, ' Cat. of Mus. Pract. Geol.' (name only). 

 1868. „ „ Bigsby, ' Thesaur. Silur.' (name only). 



Type. — The rate of increase is 2.5, and the last whorl is .5 of the whole. The 

 section is rounded sagittate, being very flat on the sides, and narrow on the convex 

 border, the greatest thickness being near the inside, but the amount is not 

 measurable. Almost the whole surface exposed is smooth, but on the earlier part 

 of the last whorl are some fine radial lines, and the inner whorls are not properly 

 preserved. The body-chamber extends for nearly ^ a whorl, but shows no change 

 at the aperture. The septa are uniformly curved throughout, and are distant about 

 \ of the diameter of the whorl, where seen. No siphuncle is exposed. The 

 greatest diameter is 6^ inches. From the Lower Ludlow of Ledbury. In the 

 collection of Dr. Grindrod. 



General Description. — The rate of increase and breadth of the last whorl vary 

 very little in the different examples ; the greatest breadth is .54. The section may 

 be more or less due to compression, as all examples are more or less imbedded in the 

 stone. The shape is always as in the type in adult forms, but more quadrate in the 

 young, the maximum thickness observed being ^ the breadth. On the outer whorl 

 of some are seen slight undulations of growth towards the inner side, and a few 



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