328 THE LIAS AMMONITES. 



principal lateral lobe, is formed of two large unequal leaves, of which the internal one is 

 the largest, and both are very much divided ; the principal lateral lobe terminates in two 

 large very much ramified branches. D'Orbigny was however unable to follow the others, 

 as shown in his excellent drawing of the lobe-line which I have copied from his work 

 in my fig. 4, PI. XVIII. 



Affinities and Differences. — M. Eug. Dumortier has figured, in his ' Depots 

 Jurassiques du Bassin du Rhone,' pi. xxx, figs. 1 and 2, a fragment found at Jambles, 

 Saone-et-Loire, which agrees very w r ell with the specimen I have figured in PL XVIII, 

 fig. 1, from the Rev. J. E. Cross's collection; the sides are convex; the siphonal area 

 narrow, and furnished with a round carina, which is absent from the mould. 



Professor Quenstedt has figured and described, ' Der Jura,' p. 98, pi. xii, fig. 7, a 

 fragment from his " Beta " limestone of Ofterdingen, under the name detacalcis, and 

 this comes from the same horizon as A. Boucaultianum. It has many affinities with our 

 large specimen ; the crenulated carina appears to separate it from A. Boucaultianum ; 

 still it must not be forgotten that this is a single unique specimen, and that some of 

 the type specimens in the Semur Museum, with their shell preserved, measuring from 

 twelve to fifteen inches in diameter, show a disposition to a like crenulation on the 

 central portion of the siphonal area, so that I am inclined to think that Quenstedt's 

 fragment, when better specimens are found, may turn out to be a true A. Boucaultianum. 



Localities and Stratigraphical Position. — The Rev. J. E. Cross, F.G.S., collected his 

 specimen, the only British one I know, from the Upper Bucklandi-beds of the Scunthorpe 

 Ironstone, North-west Lincolnshire. A suite of several very fine specimens has been 

 obtained from the Lower Lias near Semur, Cote-d'Or, and is in the Museum 

 of that town. One noble Ammonite, with its shell preserved, which I measured, was 

 upwards of twelve inches in diameter. PL XVIII, figs. 2, 3, represent a specimen 

 reduced one third the natural size, in the collection of Monsieur Boucault of Semur, who 

 collected it at Champlong, near that town. Several important characters of this rare 

 Ammonite are here very well shown. I am indebted to my friend, M. Collenot, of 

 Semur, for two specimens of this Ammonite, which he has kindly sent me to complete my 

 description of the species. The largest specimen is 185 millimetres in diameter, the 

 height of the aperture is 110 millimetres, its width 50 millimetres, and the diameter of the 

 umbilicus 23 millimetres ; the twenty-six lateral primary ribs are well seen ; at the umbilical 

 margin they bifurcate irregularly at about one third the height of the whorl, and toward 

 the aperture become thickened at the side of the siphonal area and develop a tubercle on 

 each ; the centre of the area is narrow and flattened, and the ribs pass from one side to the 

 other (fig. 3). The shell is preserved on a small portion only of a larger specimen, but 

 enough remains to enable me to make out its remarkable structure; the shell is very 

 thin, and bears a delicate sculptured surface, with lines following the flexure of the 

 ribs, as is very well exhibited in PL XVIII, figs. 1 and 2 ; the lines, however, are much more 

 delicate in the specimens sent me by M. Collenot than in those represented in d'Orbigny's 



