380 
MOLLUSCA. 
inches two lines long. Fossil, East Indies; and in Mount St 
Catharine, near Rouen. 
Genus 9. — ORBULITES.— Lamarck. 
Generic Character. — Shell subaiscoid, 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 LXXXI1I. fig. 6. 
Umbilicated; volutions hidden, transversely and minutely 
striated and ribbed; back acute. One and a half inches long. 
Fossil. 
Genus 10. — A MM O NITE S. — Lamarck. 
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 LXXXIII. fig. 7. 
Subcarinated, yolutions depressed at their inner margins; 
with strong transverse striae and clavate ribs. Fossil. 
TRIBE 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.— Linnaeus. 
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 umbilicatus. — The Umbilicated Nautilus. 
Plate LXXXIII. fig. 8. 
Suborbicular; the centre of the volutions umbilicated; aper¬ 
ture round, heart-shaped; pale fawn-coloured, with chestnut 
