imperfectly- defined Species of Jurassic Nautili. 289 



Sp. char. Shell subglobose, compressed on the sides and 

 periphery, the latter at first narrow and considerably flat- 

 tened, but in the later stages of growth becoming wider and 

 more rounded. The umbilicus is very large in proportion to 

 the shell-diameter, its greatest width being H inches, while 

 that of the shell is about 5 inches ; it is moderately deep and 

 exposes all the inner whorls, the sides slope steeply, and the 

 outer border is subangular. The test, which is admirably 

 preserved, is thick, and its surface is marked only with fine 

 lines of growth, which make a deep sinus upon the periphery 

 (see fig. 17, b). The septa arc rather wide apart ; the sutures 

 slightly sinuous on the sides of the shell and forming a slight 

 sinus on the periphery. In a young shell (2j inches in 

 diameter) the inner lobe is very conspicuous. The siphuncle 

 is a little below the centre. 



Remarks. This fine species is unlike any other known to 

 us in the Jurassic rocks, but it bears some resemblance in the 

 character of its umbilicus to the recent Nautilus umbilicalus, 

 from which species it differs, however, in the proportionately 

 greater size of its umbilicus and more flattened periphery. 



Horizon. Inferior Oolite. 



Locality. Burton-Bradstock, Dorsetshire. 



Middle Oolite. 



17. Nautilus calloviensis, (Jppel. 



r 1840. Nautilus hexaff onus?, .1. de ( '. Sowerby, in Grant's Fossils of 



Cutch, in Trans. Geol. Soc. ser. ii. vol. v. pt. ii. p. ■Vi'-.), pi. xxiii. 



tig. 4 (not of Sowerby ). 

 L842. Nautilus hexagonus, d'Orbigny, Paleontologie Francaise, Terr. 



Jurass. vol. i. p. 161, pi. xxxv. rigs. 1, 2 (not of Sowerby j. 

 L858. Nautilus calloviensis, (Jppel, l)ie Jurafornaation Englands, Frank- 



reichs ivnd des siidwestlichen Deutschlands, p. ;147. 

 1875. Nautilus calloviensis, Waagen, Mem. ({col. Surv. India, Palseont. 



Iudica, Jurassic Fauna of Kutcli, vol. i. p. Is, pi. Hi. figs. 2, a, b. 

 L884. Nautilus calloviensis, Lahusen, Memoires du Comite" Geologique 



[Russia], vol. i. no. 1, p. 42, Taf. iii. figs. 28, a, b, and 29, a, b 



(young). 

 L884. Nautilus hexaffonus, Mallada, Boletin do la Comision del Mapa 



Geolugico do Espana, Sinopsis do las Especies Fosiles de Espana, 



vol. xi. p. 22 ( .) (figured 187.8, vol. v. pi. iv. tig. 9). 



Sp. char. General form cf the shell somewhat compressed, 

 smooth, or marked only by faint, very fine, close-set lines of 

 growth. The whorls are obtusely angular, flattened at the 

 sides, and broadly truncated upon the periphery, the greatest 

 thickness being at the umbilical margin. The umbilicus is 

 very small. The septa form a sigmoid curve upon the shlos 

 of the shell and are slightly sinuous upon the periphery. 



