124 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



another, 'No. C. 4493 (i), the more inflated form, and a third, No. 

 C. 4492 (ii), is prohahly a young shell of the latter. The amount of 

 inflation is prohahly due merely to a difference in sex, in which case the 

 more inflated form is the male, and the other the female. It may also be 

 noted that the peripheral sinus of the suture-line is deeper in the less 

 inflated than in the other form. The largest specimen (53'5mm. in 

 diameter) has the last two septa very approximate, and is probably an 

 adult shell. All the specimens are from the same locality and horizon. 



The British Museum Collection contains a specimen (No. 37,023) 

 from the "Great Oolite, Ranville, Normandy," that may possibly 

 belong to this species. It is larger than the British specimens, its 

 dimensions being : — Diameter, 57 mm. ; height of outer whorl, 34 mm. ; 

 ditto above preceding whorl, 28 mm. ; thickness, 37 mm. ; width of 

 umbilicus, 5 mm.; width of periphery at greatest diameter, 31mm. 

 It is more inflated, and has a smaller umbilicus than the British 

 compressed form, hut its periphery is relatively narrower than that 

 of the inflated form. 



Form, and Loc. — Inferior Oolite : Burton Bradstock, Dorset. 

 Mr. Buckman considers the three specimens referred to this species 

 to have come from the " upper :ZVMe//e^-beds of Burton Bradstock." 



4. Nautilus subsinuatus, D'Orhigny. T?igs. VI & VII. 



Nautilus sinuatus, J. Sowerby: Min. Conch., vol. ii (1818), p 231, 



pi. cxciv. 

 Nautilus sinuatus, J. Shy. : A. d'Orbigny, Pal. Franq. Terr. Jur., 



vol. i (1842), p. 157, pi. xxxii. 

 Nautilus suhsinuatus, A. d'Orbigny: Prod, de Paleont. stratigr., vol. i 



(1850), p. 260. 

 Nautihis sinuatus, J. Shy. : E. Eudes-Deslongchamps, Jura Normand, 



Monog. vi (1877), pi. viii, figs. 1-3. 



Specific Characters. — Shell compressed, somewhat rapidly increasing ; 

 greatest thickness close to the umbilical margin, a little less than one- 

 half of the diameter of the shell; height of outer Avhorl rather more 

 than four -sevenths of the diameter of the shell. Whorls three or four ; 

 inclusion nearly complete, about three-fourths in the outer whorl; 

 umbilicus small, about one-eleventh of the diameter of the shell in 

 width, with subangular margin and steep, slightly overhanging sides. 

 "Whorl subsagittate in section, rather higher than wide ; indented to 

 about three-elevenths of its height by the preceding whorl ; periphery 

 obtusely rounded ; sides flattened, very feebly convex ; inner margin 

 distinct, convex, slightly overhanging the umbilicus. Length of body- 

 chamber not seen. Chambers not very deep, their depth at the 

 periphery being rather less than one-half of the corresponding height 

 of the whorl ; suture-line with a deep sinus on the lateral area, about 

 one-third of the corresponding height of the whorl in depth, almost 

 straight on the periphery. Test smooth on the lateral area, ornamented 

 on the peripheral area with moderately fine longitudinal raised lines, 

 which in the young shell extend a little over the lateral area ; sides of 

 the umbilicus also with concentric coarser longitudinal raised striae. 



