LYTOCERAS JURENSE. 413 



Lytoceras Jurense, Zieteii. PL LXXIV, figs, 3 — 5 ; PI. LXXIX. 



Ammonites Jurensis, Zieten. Versteiuer. Wiirtemb., p. 90, tab. Ixviii, fig. 1, 1830. 



— — d'Orbignij. Pal. Frangaise Ter. Jurass., p. 318, pi. 100, 1842. 



— — Quenstedt. Flozgebirge Wiirtemb., p. 269, 1843. 



— — — Cephalopoden, p. 104, tab. vi, fig. 7, 1849. 



— GVhE^Hki'oii, Simpson. Mon. Amm., p. 17, 1843. 



— Jurensis, Giebel. Fauna der Vorwelt, Bd. iii, p. 406, 1852. 



— — Morris. Catalogue of British Fossils, 2nd ed., p. 292, 1854. 



— GUBERNATOR, Si'm^wo?;. Foss. York. Lias, p. 40, 1855. 



— Jurensis, Quenstedt. Der Jura, p. 279, tab. 40, fig. 1, 1858. 



— — Brauns. Der Mittlere Jura, p. 104, 1869. 



— — Bumortier. Depots Jurassiques, partie iv, p. 109, 1874. 

 Lytoceras Jukense, Neumayr. Zeitsclir. Deut. geol. Gesellsch., Bd. xxvii, p. 893, 



1875. 



— — Tate and Blake. Yorkshire Lias, p. 298, 1876. 



Diagnosis. — Shell discoidal, compressed ; whorls half involute ; sides flattened, and 

 bevelled away towards the umbilical suture ; siphonal area convex ; shell ornamented with 

 very fine lines of growth ; mould smooth without a trace of shell-lineation ; suture-line 

 very complicated. 



Dimensions. — Some German examples attain a diameter of two feet. One example 

 in my collection from the Lias at Wasseralfingen, and only the inner portion of a large 

 shell, is 155 millimetres in diameter; the inner whorls are convex and flat, and the 

 outer whorl expands largely and abruptly with a deep concave slope towards the 

 umbilicus. The small specimen, PI. LXXIV, figs. 3 — 5, is 105 millimetres in 

 diameter ; the height of the aperture is 50 millimetres, and its width 32 millimetres. 



Description. — Thirty years ago I collected this Ammonite from the Liassic sands of 

 Frocester Hill, where a few individuals at that time were found. My original specimens 

 were mislaid and lost soon after they were discovered, and the species was not again met 

 with until 1880, when three or four rough examples were re-discovered in the same 

 locality, and these have served to prove that the Jurense-zo\\& exists in the Cotteswold Hills. 



The shell is discoidal and compressed ; the whorls, which rapidly increase in height, 

 are one half involute ; they are flattened or slightly convex on the sides, and bevelled 

 away towards the umbilical suture, a character which serves to distinguish this species 

 from Lytoceras oolif/iicu7ii,d'0rh., an inferior oolite species with which it has many affinities. 

 The siphonal area is extremely convex. The shell is extremely thin, and seldom preseryed. 

 When found it is seen to be ornamented with numerous very fine lines of growth that 

 leave no mark on the mould, which is quite smooth. The sutural line (fig. 3) is very 

 complicated. The siphonal lobe is one third shorter and as wide as the principal lateral. 



