68 CEPHALOPODA. 



Genus 5.— ARGONAUT A.— LmncBus. 



Generic Character. — Shell spiral, univalve, unilocular^ and 

 membranaceous ; doubly carinated. 



Argonauta argus. — The Argus Argonauta, or Paper 

 Nautilus. — Plate X. fig. 2. Shell white, involute, extremely 

 fragile, sides with undulated ridges, and obsoletely striate ; keel 

 with small tubercles. Inhabits the Mediterranean. 



Sub- Division III. — Cephalopoda Polythalama. 

 Shell multilocular, partly or wholly internal, and enveloped 

 in the posterior part of the body. 



FAMILY I. AMMONACEA. 



With the septa sinuous, lobed and cut at the margin, meeting 

 upon the inner wall of the shell, and articulated by acutely 

 notched sutures. 



Gemis 6.— BACULITES.— Zamarc^. 



Baculltes Faugusii. — Faugus's Baculites. Plate X. fig. 3. 

 Erect, cylindrical, opposite sides smooth and depressed; su- 

 tures with lobed dentations. 



Genus 7.— TURRILITES.— ZawjarcA. 



Generic Character — Shell spiral, turrited, volutions contigu- 

 ous, and all conspicuous ; partitions articulated with sinous su- 

 tures ; septa transverse, lobed, and laciniated at the margin ; 

 aperture nearly round. 



Turrilites costulata. — The Ribbed Turrilites. Plate X. 

 fig. 4. Erect, turrited ; volutions convex, with transverse ribs 

 each with a tubercle at its base. 



Genus 8 AMMONO CERATITE S — Lamarck. 



Generic Oiaracter. — Shell horn-shaped, arcuated, subsemi- 

 circular ; the partitions articulated with sinous, laciniate, branched 

 sutures ; septa transverse, sinous, imperforate ; their margins 

 lobed, laciniate ; having a marginal tube or syphon, which does 

 not perforate the septa. 



Ammunoceratites glossoidea — The Glossy Ammonoceratites. 

 Plate X. fig. 5. Large, thick, cylindrical, arcuated, lateral, 



