MULTILOCULAR SHELLS. 255 



the mouth, till they entirely disappear. The ribbed part indeed is 

 wanting in most specimens. The whole shell, both where it is ribbed 

 and where it is plain, is striated from the umbilicus outwards, the 

 striae being continued round the back ; bvit very often the shell is 

 partially gone, and the foliated edges of the septa, which are arranged 

 in the most elegant form, are displayed in all their beauty ; as may 

 be seen in part of the specimen figured. This nautilus, like the 

 former, is found in our aluminous strata, particularly in the main bed 

 of alum shale. The siphuncle runs along the back, in which respect, 

 and in the aperture, it differs from Sowerby's n. truncatus. Tab. 123 ; 

 which, however, by his own account, was figured from fragments of 

 different specimens, part of which, we suspect, might coincide with 

 our shell. As there is nothing truncate in our fossil, we shall 

 name it n. Whithiensis. 



Fig. 7, PI. XII, represents a rare and handsome umbilicated nau- 

 tilus, also from the alum shale. It is distinguished by a flat space 

 running along the back, divided in the middle by a slight ridge, or 

 imperfect keel. The sides are marked with fine striae, and with 

 irregular undulations ; and the edges of the septa, where exposed, are 

 beautifully foliated. This species is not so flat as n. Whitbiensis, 

 nor so globose as n. pompilius, and is much smaller than either. N. 

 lineatus of Sowerby, Tab. 41, resembles it, but is obviously another 

 species. From its imperfect keel, we may designate our shell n. 

 suhcarinatus. 



Polished sections of nautilites or ammonites, from the aluminous 

 strata, are often very beautiful and interesting ; the chambers being 

 filled with a light coloured spar, while the septa and exterior shell 

 are of a darker colour. The mixture of pyrites sometimes adds to 

 their beautj% though the highly pyritous specimens do not take a 

 good polish. In some sections, particularly those of the lobster- 

 tailed nautilus, the siphuncle is finely displayed. 



