﻿210 BRITISH FOSSIL CEPHALOPODA. 



Group III. Spirales. 



Genus Nautilus. 



Nautilus bohemicus, Barrande, PL XXVII. figs. 1, 2. 



' 1865. Nautilus bohemicus, Barrande, ' Syst. Silur. de Boheme,' vol. ii. pi. 32, 33, &c. 

 Syn. 1838. Lituites Biddulphii, Sowerby in Murchison's ' Silurian System,' pi. 11, fig. 8. 

 1865. Nautilus tyrannus, Barrande, loc. cit., plates 38, 39, 40. 

 1865. Exosiphonites Edgellii, Salter, ' Cat. Foss. Mus. Pract. Geol.' (name only). 



Type. — The figures given by Barrande of the two species quoted above show- 

 that some variation must be allowed in the dimensions, and I am constrained to 

 regard the whole series as forming but one species. Certainly the fragmentary 

 English specimens might equally well be referred to one or to the other. The rate 

 of increase is given by the author as 2 for the first, and 1.75 for the second ; but the 

 figures show a variation between 1.8 and 2.5 for the first, and 1.8 and 2.1 for the 

 second. The breadth of the last whorl varies in the one case from .42 to .56, and in 

 the other from .47 to .5 ; the greatest difference being in the larger examples. The 

 section is an elongated oval, rather flat on the sides and back ; the greatest thickness, 

 which is near the umbilicus, is said by Barrande to be ^ the breadth, but none of the 

 figures indicate it so small. The surface shows only backward-curving lines of 

 growth, forming a sinus on the convex side. The body-chamber is less than ^ a 

 whorl. The aperture is simple and parallel to the lines of growth. The septa 

 are about ^ to \ the diameter of the whorl apart, and from \ to \ convex. The 

 sutures are concave on the sides, and bend forward on the front. The siphuncle is 

 a little beyond the centre towards the outside. 



General Description. — Only fragments have as yet been found, but these are 

 highly characteristic. The dimensions, however, are not satisfactorily ascertainable, 

 but the shape of the figured specimen, as well as its size, agrees almost exactly with 

 the drawing given by Barrande on his plate 40, referred to a large N. tyrannus. 

 The whorls slightly overlapped, as shown by the concavity of the inside of the 

 section. The section is elongate, roundedly subquadrate, with a thickness about 

 I the breadth. The ornaments are no more than lines of growth, sometimes 

 pretty regular ; they curve rapidly backwards so as to come to a sinus on the 

 convex side ; on what is probably an inner layer, these are found more crowded, 

 upstanding and crinkled. Some have abundant transverse epidermids on the 

 cast, viz. on the inner side of a body-chamber, 12 per line, but one specimen 

 shows some in a longitudinal direction. The body-chamber extends to nearly 



