AEGOCERAS JOHNSTON! 311 



is not found in situ at low-water mark. The fine specimen, now in the Woodwardian 

 Museum, figured in PL XIV, fig. 1, was broken out of one of these boulders. 



Foreign Distribution. — In Wurtemburg it is found in fine preservation at Nellingen 

 and Riedern, near Esslingen, at Bebenhausen, near Tubingen, and in the vicinity of 

 Rottweil. In France at Saulieu, and Beauregard, Cote d'Or, where it is associated with 

 Aeg. Johnstoni, Sow., Aeg. laqueus, Quenst., and Aeg. Burgundies, Mart. ; it is found like- 

 wise at Avallon, Yonne. 



Aegoceras Johnstonii, Sowerby, 1824. PI. XIX, figs. 3, 4. 



Ammonites Johnstonii, Sowerby. Mineral Conchology, vol. v, p. 70, tab. 449, fig. 1, 



1824. 



— tobtjs, d'Orbigny. Pal. Franc,., Terr. Jurass., p. 212, pi. liii, 1842. 



— Johnstoni, Oppel. Juraformation, p. 74, 1856. 



— — Giebel. Fauna d. Vorwelt, vol. iii, p. 738, 1852. 



— — Neumayr. Fauna der untersten Lias d. Nordalpen, p. 29, 



pi. iii, fig. 2, 1879. 

 Aegoceras — Tate Sf Blake. Yorks. Lias, p. 271, 1876. 



Diagnosis. — Shell discoidal, compressed ; whorls, from eight to ten, depressed ; sides 

 convex, with thirty simple, short, oblique ribs, which occupy only the middle of the 

 whorl, and are not developed on the inner or outer margins ; siphonal areas rounded, and 

 smooth ; aperture subrotund. 



Dimensions. — Diameter 90 millimetres ; ditto of the umbilicus 58 millimetres ; height 

 of the last whorl 18 millimetres ; width of ditto 17 millimetres ; septa five-lobed. 



Description. — Although this species is often quoted in lists of Lower-Lias Fossils, 

 good specimens are extremely rare. I could not find one for figuring in either of the 

 metropolitan Museums nor in those of the Midland Counties, where it is said to be common. 

 Sowerby 's original type belonged to Mr. Johnstone's cabinet, and was extracted from the 

 slaty shales of the Lower Lias at Watchet, where it lies associated with Aegoceras planorbis. 

 It is almost always much compressed, and the shell wants its outer lamina ; the pearly 

 inner layer is very brilliant and full of iridescent colouring. "When the fossil is not 

 compressed it assumes a different appearance, and comes out as Am. torus, d'Orbig., of 

 which I have figured a typical specimen from Professor Deslongchamps' collection at 

 Caen. This specimen is compressed, discoidal, and not carinated ; the whorls are nume- 

 rous, regular, and exposed (fig. 3), the spire consisting of nine whorls, which are 

 extremely regular, and ornamented with thirty short simple ribs that occupy only the 

 convex middle portion of the whorl ; they do not extend either to the outer or inner 

 margins of the same, and are wholly limited to the flanks ; the other parts being smooth 

 and destitute of ribbing. The siphonal area (fig. 4) is rounded and quite smooth, having 



