326 THE LIAS AMMONITES. 



number, diminish in size from without inwards as they approach the columellar suture, 

 and a radial line, drawn from the point of the siphonal lobe inwards to the first auxiliary, 

 cuts the termination of the principal lateral, and leaves all the other portions of the septa 

 much in advance. 



Affinities and Differences. — Aegoceras Charmassei very much resembles Aeg. angu- 

 latum in youth and middle age, but in old age the whorls are much higher, and the 

 lobe-line is very different. It resembles Aeg. catenatmn in youth in its general outline, 

 but still its ribs are bifurcated, whilst those of Aeg catenatmn are simple. It has certain 

 affinities with Aeg. Boucaultianum in the height of its whorls, and in the ribbing of the 

 same. Aeg. Boucaultianum, however, has many more small close-set ribs, with a flatter 

 area, tuberculated on the sides, and with a different and more complicated lobe-line than 

 Aeg. Charmassei. I know of no other forms with which this beautiful Ammonite has any 

 close relations. The Rev. J. E. Blake, F.G.S., 1 notes " This appears to me a protean species, 

 whose varieties are extreme . . . There is (a) an inflated variety, whose cross section 

 is a transverse rounded rectangle, with great inflated ribs, and whorls scarcely overlapping, 

 not growing to above two inches in diameter ; ((5) the ordinary form flatter and larger 

 (six inches) ; (y) a far more involute form, with the outer whorl half the diameter, as 

 figured by Dumortier ( f Depots Jurassiques,' part i, pi. xvii, figs. 1 and 2); (S) the 

 large adult shell nearly smooth, as figured by d'Orbigny (pi. xcii). The variety 

 a includes the A. crenularis of Simpson ; variety y is the A. Boucaultianus of d'Orbigny. 

 The Yorkshire specimens have so decided a connection with Aeg. Charmassei as to force 

 me to include them under the latter name. More characteristic forms of A. Boucaul- 

 tianus have been found by Mr. Cross in Lincolnshire. The A. anliquatus of Simpson is a 

 fragment of the adult shell ; while A. sulcatus {A. Leignelettei, d'Orb.) is the young of 

 the ordinary form. Simpson's name, A. sulcatus, would have preference of A. Char- 

 massei, by which the species is well known, only fortunately the former name was 

 preoccupied by Lamarck." 



Localities and Stratigraphical Position. — This species is found in the zone of Arietites 

 Buchlandi at Redcar and Robin Hood's Bay, Yorkshire, and in beds of like age at 

 Charmouth, and Lyme Regis, Dorset, and at Portrush, near Londonderry, on the north 

 coast of Ireland. In Erance, it is found with Grgphaa arcuata in the centre of Erance, 

 and has been collected in the Lias quarries at Avallon, Yonne; near Semur, and Clomot, 

 Cote-d'Or ; and at Drevain, Saone-et-Loire. 



In South Germany it is found in the Lower Lias between the zone of A. planorbis and 

 that of A. Buchlandi at Ostdor by Balingen, near Aich, Echterdingen, Degerloch, 

 Vaihingen, Bebenhausen, Bemflingen, Goppingen, Metzingen, Kaltenthal, near Stuttgart, 

 Wurternberg. 



1 ' Yorkshire Lias,' p. 2/2. 



