12 FOSSIL MOLLUSCA OF THE CHALK. 



abundant in the Chalk with sihceoiis grains at Chaldon and Man-of-War Cove in Dorset- 

 shire, and Chardstock in Somersetshire. M. D'Orbigny cites it from the Craie Chloritee 

 of ]\lount Ste. Catherine, near Rouen. 



The figure in the ' Mineral Conchology ' is taken from a specimen somewhat expanded 

 at the mouth by pressure ; but the form of the umbilicus and the fine sharp striae leave no 

 doubt of its identity with N. Archiacianus, D'Orb. 



3. Nautilus Deslongchampsianus, If Orb. Plate HI, figs. I and 2. 



Nautilus elegaxs, part. Mantell. Fossils of the South Downs, t. xxi, fig. 8. 

 — Deslongchampsianus, D'Orbigny. Paleont. Fran9. Terr. Cret., t. xx. 



N. testa s^ib-glohosd, umhilicatd, transversim costatd et longitudinaliter striatd; wnbilico 

 carinato ; costis elatis jlexuosis ; striis tenuihus dectissatis ; aperturd semi-ovali. 



Shell sub-globose, umbilicated, elegantly ornamented with sharp elevated transverse 

 flexuous ribs, which are usually crossed by thin longitudinal lines ; the latter are often 

 obliterated in ill-preserved casts ; the ribs rise within the umbilicus and are bent at a 

 sharp angle over its carinated margin ; they then sweep forward in a bold curve, and form 

 a deep sinus on the back, where they occasionally divide into two ; the ribs are steep on 

 their front side and sloping behind, thus forming a series of steps on the surface ; the edge 

 of the umbilicus is angular or raised into a slight keel. 



The longitudinal lines are very prominent in some specimens, but can hardly be 

 discerned in others ; but the species can always be distinguished by the form of the ribs, 

 the deep and angular umbilicus. It is common in the Grey Chalk of Lewes, Dover, the 

 Isle of Wight, &c., and in the Chalk with siliceous grains of Chardstock, Somersetshire. 

 In France it abounds in the Craie CJdoritee of Mount Ste. Catherine, near Rouen. 



Diameter 2i inches, breadth If inch. 



4. Nautilus elegans, Sowerbt/. Plate HI, fig. 3 ; and Plate IV, fig. 1. 



Nautilus elegans. Sowerby. Min. Con., t. 116. 



— — Mantell. Fossils of the South Downs, t. xx, fig. 1 . 



— — D'Orbigny. Paleont. Fran9. Terr. Cret., t. xix. 



N. testa globosd, costatd ; costis cequalibus, rotundatis, suh-jlexuosis ; aperturd semi- 

 circulari ; siphunculo inter dorsum et septi centrum posito ; umbilico minimo. 



Shell globose, uniformly rounded, ribbed ; umbilicus slightly marked on the outer but 

 entirely concealed in the inner whorls ; ribs equal, rounded, and regular, bending in a 

 simple curve from the umbilicus to the back, where they form a broad shallow sinus ; 

 aperture semi-oval, a little higher than broad, deeply indented by the preceding whorl. 

 Siphuncle placed about half way between the centre of the septum and the back. 



