340 THE LIAS AMMONITES. 



Locality and Stratigrapliical Position. — The figured specimen was collected at 

 Lyme Regis ; it is embedded in a grey Lias Limestone which occurs about the base 

 of the Middle Lias. I had no other specimen from the same bed to check my diagnosis, 

 but it is apparently the base of the Aegoceras Jamesoni-zonQ. I have not seen another 

 specimen in any of the collections I have consulted. 



Aegoceras armatum, Sowerhy. PI. XXVIII, figs. 1—6 ; PI. XXIX. 



Ammonites armatus, Sowerby. Mineral Conchology, vol. i, tab. 95, p. 215, 1815. 



— — Toung and Bird. Yorks. Coast., p. 249, pi. xiii, fig. 9, 1822. 



— HASTATUS, Toung and Bird. Ibid., pi, xiv, fig. 2, 1822. 

 Planites fibulatus, Haan. Amm. et Gonial., p. 84, No. 8, 1825. 



Ammonites armatus, d'Orbigny. Paleontol. Fran9aise ; Ter. Jurass., p. 2/0, pi. 78, 



1842. 



— — Quenstedt. Flozgebirge Wiirtembergs, p. 157, 1843. 



— — Simpson. Monograph on York. Lias Aramon., p. 26, 1843. 



— — Quenstedt. Cephalopoden, p. 82, 1849. 



— — Oppel. Juraforraation, p. 155, 1856. 



— — Simpson. Fossils of York. Lias, p. 64, 1855. 



— miles, Simpson. Ibid., p. 65, 1855. 



— armatus, Schlbnbach. Mittleren Lias, Zeitschrift Deutsch. geol. Gesell- 



schaft, p. 511, Jahr 1863. 



— — Bumortier. Depots Jurass. du Bassin du Rhone, vol. iii, 



p. 59, pL viii, figs. 1, 2, 1869. 



— — Emerson. Die Liasmulde von Markoldendorf, Zeitschrift 



Deutsch. geol. Gesell., p. 330, pi. x, fig. 4, 1870. 

 Aegocebas armatum, Tate and Blake. Yorkshire Lias, p. 277, 1876. 



Diagnosis. — Shell large, compressed ; whorls slightly involute, umbilicus wide, and 

 inner whorls all exposed ; spire formed of from six to eight volutions ; the outer whorl, 

 according to age, with from eighteen to twenty ribs, which arise from small striae at the 

 umbilical suture, and enlarge as they advance towards the margin of the siphonal area, 

 where they terminate in long, stony, tubular spines ; between the principal ribs, and 

 on the spines themselves, are other smaller transverse striae ; siphonal area wide, 

 flattened, slightly convex, and ornamented transversely with a continuation of the same 

 striae that adorn the sides ; spire composed of rounded or subquadrate whorls somewhat 

 depressed and inclined towards the umbilicus ; aperture subquadrate, the transverse 

 exceeding the vertical in diameter. 



Dimensions. — Transverse diameter 115 millimetres; width of umbilicus 55 milli- 

 metres ; height of the aperture 30 millimetres ; width 36 millimetres. 



Description. — Much confusion appears to have existed among the local palaeontologists 

 of Yorkshire, where this Ammonite was first discovered, regarding the figure and 



