HARPOCERAS INSIGNE. 453 



Harpoceras insigne, Schilbler. PI. LXV, figs. 1 — 6 ; PI. LXVI, figs. 1 — 3. 



Ammonites insignis, Schubler in Zieten, Verst. Wiirtemb., p 20, tab. xv, fig. 2, 



1830. 



— — Quenstedt. Flozgebirge Wiirtemb., p. 272, 1843. 



— Phillipsii, Simpson. Monog. Ammonites, p. 36, 1843. 



— insignis, Quenstedt. Cepbalopoden, p. 97, 1849. 



— — d'Orbigny. Paleont. Francaise, Terr. Jurass., p. 347, tab. 



112, 1842. 



— Phillipsii, Simpson. Foss. of Yorksh. Lias, p. 78, 1855. 



— insignis, Oppel. Die Juraformation, p. 250, 1856. 



Quenstedt. Der Jura, p. 280, pi. 40, figs. 4, 5, 1858. 



— — Dumortier. Depots Jurassiques, partieiv, p. 74, pis. xvii, xviii, 



1874. 

 Harpoceras insigne, Tate and Blake. Yorkshire Lias, p. 310, 1876. 



Diagnosis. — Shell discoidal, depressed, and carinated ; volutions six, one half invo- 

 lute ; whorls convex on the sides, a row of tubercles developed at the angle near the 

 inner margin, from which round l'asciated ribs, slightly bent forward, proceed to ter- 

 minate by the side of the carina ; a short single rib lies in general between each pair of 

 fasciated ribs ; carina large, round, and not prominent ; in youth and middle age the whorls 

 are round; in large specimens the outer whorl becomes triangular, PI. LXVI, fig. 2. 



Dimensions. — The specimen figured on PI. LXV, fig. 1, transverse diameter 133 

 millimetres ; width of the umbilicus 53 millimetres ; height of the aperture 40 milli- 

 metres ; width 35 millimetres. This shell may be considered as a good typical example 

 of the middle period of life of this species. By far the finest example of this species is 

 that contained in the Museum of Geneva. The specimen was collected from the iron 

 stone either of Thouars Deux-Sevres or of La Verpilliere, and is figured in PI. LXVI, 

 figs. 1 — 3. Its dimensions are transverse diameter 290 millimetres ; amount of 

 involution two thirds the height of the whorl ; the width of the umbilicus 100 millimetres ; 

 height of the aperture 114 millimetres; width of aperture near the base 110 millimetres. 

 In this grand specimen the siphonal area forms a trigon, as is very well seen in the 

 transverse section of the aperture. 



Description. — I have figured three varieties of this Ammonite. PI. LXV, fig. 1, I 

 consider a good type form of this species during middle life. The shell is discoidal, 

 the sides depressed, and the area supports a thick round keel, towards the sides of which 

 the costae approach and terminate (rigs. 2, 3) ; the volutions, six in number, are one half 

 involute, the sides are convex, and on the inner margin near the angle there is a row of 

 round prominent tubercles, from each of which a fasciculus of round costae, slightly 

 inflected forward, pass over the sides toward the siphonal area, increasing in thick- 



