XAniLIDJS. 
267 
1852. Xaufilus triamjidaris, Giebel, Fauna der Vorwelt, Band iii. 
Abth. i. p. 162. 
1854. Naidilus triangularis, Millet, Paleont. de Maine-et-Loire, p. 103- 
1859. Xautihis triangularis, Pictet et Campiche, Description des Fos- 
siles du Terrain Cretace des Environs de Sainte-Croix (Paleon- 
tologie Suisse), sG\ ii. pt. i. pp. 141, 149. 
1861. Nautilus triangularis, Revues, Etudes sur le Synchronisme et la 
Delimitation des Terr.-Cretaces du Sud-Est de la France, p. 41. 
1866. Nautilus triangularis, Beltreinieux, Fauue Fossile du Departe- 
ment de la Charente-Inferieure, pp. 43, 80. 
1890. Nautilus triangularis, Foord and G. C. Crick, Ann. Mag. Nat. 
Flist. ser. 6, vol. v. p. 403. 
Sp. Char. “Shell compressed, smooth, with the periphery 
alternately rounded and sharply angular ; umbilicus closed ; section 
triangular, the sides very slightly rounded, deeply emarginated by the 
preceding whorl. Septa considerably curved upon the sides, and pro- 
jecting forwards upon the peripheral angle, slightly bent backwards 
in the umbilicus. According to d’Orbigny the siphuncle is situated 
below the centre, not far from the ventral border. Test unknown. 
Remarks. “ This species is readily distinguished from Nautilus 
Fleuriausianus, d'Orbigny, as figured and described in the Pal. 
Frang. (Terr. Cret. vol. i. p. 82, 1840, pi. xv.), by its sharply angular 
periphery at different stages of growth. D’Orbigny in his ‘ Prodrome ’ 
(vol. ii. 1850, p. 145) makes his Nautilus Fleuriausianus a synonym 
of the present species, but he gives no reason for so doing, and we 
have no evidence to show that N. Fleuriausianus uniiQTyvewi the same 
changes of form as those noticed in N. triangularis. These re- 
markable changes were pointed out by M. Ed. Gueranger in a paper 
read before the Geological Society of France (Bull. ser. ii. vol. vii. 
1850, p. 803), and he thus described them : — “ Dn caractere par- 
ticulier et inedit est d’avoir le dos de la spire alternativement 
anguleux ou en carene, et parfaitement arrondi ; ” . . . Stoliczka ^ 
considers also that these forms are quite distinct.” {Foord and G. 
C. Crick.) 
A remarkably fine specimen in the Collection (No. 32355) ex- 
hibits the transition from the angular to the narrowly rounded 
periphery very strikingly. This specimen is from the Upper Green- 
sand of France. 
Horizon. Lower Chalk (England). Upper Greensand (France). 
Localities. British. Sidmouth, Devonshire ; Folkestone, Kent. 
Foreign. Escragnolles (Yar), France. 
Well represented in the Collection. 
^ Mem. Geol. Surv. India — Paljeont. Indica — ser. ii. 1866, p. 207. 
