CEPHALOPODA. 59 



depressed ; inside iiatly concave ; apex compressed, tongue- 

 shaped. Nineteen inches two lines long. Fossil, East Indies, 

 and in Mount St Catherine, near Rouen. 



Genus 9.-~0RBULlTES.— Lamarck. 



Generic Character. — Shell subdiscoid, spiral, with the volu- 

 tions contiguous ; the last one enveloping the rest ; partitions 

 articulated by sinous sutures ; septa transverse, lobed at their 

 circumference, perforated by a marginal tube. 



Orhulites Striata. — The Striated Orbulites. Plate X. 

 fig. 6. Umbilicated ; volutions hidden, transversely and minutely 

 striated and ribbed ; back acute. One and a half inches long. 

 Fossil. 



Genus 10.— AMMONITES.— iawiarcA. 



Generic Character. — Shell discoid, spiral ; volutions contigu- 

 ous wholly visible ; inner partitions articulated by sinous sutures ; 

 septa transverse, lobed at the circumference, and imperforated 

 at the disc, but perforated by a marginal tube near the margin. 



Ammonites armatus. — The Armed Ammonites. Plate X. 

 fig. 7. Subcarinated, volutions depressed at their inner margins ; 

 with strong transverse striae and clavate ribs. Fossil. 



FAMILY II. NAUTILACEA. 



Shell discoid, with a central spire, and the cells short, which 

 do not extend from the centre to the circumference. 



Genus 11.— 'NAUTILUS.— LinncEus. 



Generic Character. — Shell discoid, spiral, multilocular, with 

 simple partitions ; volutions contiguous, the last or body one 

 enveloping the rest ; the septa transverse, and externally con- 

 cave, perforated in the disc ; margins entire. 



Nautilus umhilicatus. — The Umbilicated Nautilus. Plate 

 X. fig. 8. Suborbicular ; the centre of the volutions umbili- 

 cated ; aperture round, heart-shaped ; pale fawn-coloured, with 

 chestnut undulated transverse clouds. Six inches long. In- 

 habits the Indian Ocean. 



Genus 12.— NUMMULITES.— Zamarc^. 

 Generic Character. — Shell lenticular, attenuated at the mar- 



