— 154 — 
» bilis does not pass higher than the lowest fossiliferous 
» beds of the sands, both are very limited in their vertical 
» range, and never occupy the sime horizon. Both, in the 
» young and adult conditions of growth, 4. dispansus is 
» always more discoidal than the other ; the figure of the 
» back more especially differs in its acute keel, the tuber- 
» cles upon the inner margin of the volutions are much 
» more faintly marked, and unlike those of 4. variabilis 
» they are irregular ; they give origin to numerous fas- 
» ciated sygmoidal radii ; in 4. variabilis the radii consti- 
» tute rigid, nearly straight and comparatively prominent 
» ribs ; the septa in 4. dispansus have the lobes much more 
» simple, less pointed, and less produced ; the test is pre- 
» served very rarely and only in young specimens : it is 
» delicate and exhibits the fine hair like sygmoïdal radii 
» much more distinctly than the casts. » 
Localités et position stratigraphique. — Cette Ammo- 
nile est rare en Ombrie, et toujours de petites dimensions : 
mont Subasio (4 ex.), Terni (1 ex.), mont de Pale (2 ex.). 
En Angleterre, on la trouve dans la zone du Lytoceras 
jurense (Frocester-Hill). 
29. G. variabile, d'Orbigny sp. 
1843 Ammonites variabilis D’orBIGNY. Paléont. franc. Terr. 
jurass. I, p. 350, pl. CXIIT. 
1843 — Beantii Simpson. A. Monogr. of the Ammo- 
nites Yorksh., etc., p. 36. 
Diagnose. — Coquille comprimée, tours assez convexes 
sur les côtés; côtes flexueuses plus ou moins réunies en 
faisceaux qui partent d’un tubercule situé du côté interne ; 
dos aigu ; quille saillante ; ouverture comprimée, aiguë en 
avant. 
