362 THE LIAS AMMONITES. 



between ; at about the sixth volution of the spire the ribs begin to exhibit tubercles at their 

 termination by the margin of the area, and in the seventh volution the second series of 

 tubercles show themselves. In old age the volutions become less ornamented by first 

 losing the inner row of tubercles, and, secondly, by the outer row becoming smaller and 

 more rudimentary. In all these morphological changes, however, I note several points of 

 difference between the evolution of this species and that of Aeg. armatum. 



Affinities and Differences. — This species is undoubtedly closely related to Aeg. armatum, 

 but it has altogether a more slender compressed shell, with a second row of tubercles 

 on the ribs, and is more quadrate in the ensemble ; it has likewise a narrower siphonal 

 area, and a much less complicated lobe-line. Compare PI. XXVIII, fig. 6, with PI. 

 XXXIX, fig. 10, and PL XXVIII, figs. 1, 2, with PI. L, figs. 11, 12. 



Locality and 8tratigrapJiical Position. — I collected this species in the Armatus-bed at 

 the base of the Aeg. Jamesoni-zone in St. Paul's district, Cheltenham, in the Middle Lias, 

 whilst brick-earth was being dug for our town sewers. I have many beautiful examples 

 from near Charmouth, Dorset, embedded in a hard ferruginous clay -ironstone, in fact, all the 

 Armati from the Dorsetshire coast about this horizon are highly charged with ferric oxide. 

 This Ammonite was found in the Jamesoni-beds of the Island of Pabba near Skye, and 

 several specimens were collected for me from the lower beds of the Middle Lias at 

 Ballintoy, Ireland. The specimens obtained from all these widely separated localities closely 

 agree in their specific structure and petrological condition. Those from Ballintoy 

 were embedded in a hard calcareous shale. 



Aegoceras Jamesoni, Sowerby. PI. XI, figs. 4 — 6 ; PI. LI, figs. 1 — 6. 



Ammonites Jamesoni, Sowerhy. Min. Conch., vol. vi, p. 105, pi. 555, fig. 1, 



1827. 



— Bronnii, B'dmer. Nord-deutschen Oolithen-Gebirge, p. 181, 



1836. 



— Jamesoni, Quenstedt. Flozgebirge Wiirtembergs, p. 31, 1843. 



— Eegnakdi, d'Orhigny. Pal^ontologie Fran5aise ; Terr. Jurass., 



pi. 72, torn, i, p. 257, 1842. 



— Jamesoni angustus, Quenstedt. Cephalopoden, tab. iv, fig. 8, 1849. 



— — LATUS, Quenstedt. Ibid., tab. iv, fig. 1, 1849. 



— — Oppel. MittlereLias Scbwabens, Jah. Wiirtt., p. 76, 



1853. 



— Jamesoni, Oppel. Jura-Formation, p. 159, 1856. 



— — Von Hauer. Die Cephalopoden des Lias der 



Nordostlichen Alpen, pi. xix, figs. 

 1—3, 1856. 



— — lATUS, Quenstedt. Der Jura, tab. xv, fig. 15, p. 125, 



1858, 



