70 CEPHALOPODA. 



Numnmlites complanatus The Flat Ndivimulites. 



Plate X. fig. 9. Orbicular, broad, depressed at the sides, 

 and smooth ; margin undulated. One and a half inch in 

 diameter. Fossil in France, 



Genus 13 VORTICIALIS Lamarck. 



Generic Character. — Shell discoid, spiral, multilocular ; 

 volutions contiguous, but not appearing externally; septa 

 transverse, imperforate, but not extending from the centre 

 to the circumference ; aperture marginal. 



Vorticialis strigilata. — The Creased Vorticialis. 

 Plate X. fig. 9. Somewhat depressed, transversely ribbed, 

 and spirally striated. Fossil. 



Genws 14— POL YSTOMELL A.— Za;M<7rc/l. 



Generic Character Shell discoid, multilocular, with con- 

 cealed volutions ; with numerous transverse ribs ; aperture 

 formed of variously disposed holes. 



Polystomella crispa — The Wrinkled Polystomella 

 Plate X. fig. 11. Discoid, with both sides convex, the mar- 

 gin carinated ; the last turn of about twenty cells, marked 

 with flexuous ridges, having their interstices crenated. 

 Common in shell sand. 



Genus 15 SIDEROLITES.— ZawiareA-. 



Generic Character. — Shell discoid, multilocular; volu- 

 tions contiguous, but not visible externally ; the disk con- 

 vex on both sides, and studded with tubercular dots ; the 

 circumference margined with unequal radiating lobes; septa 

 transverse, imperforate; aperture distinct, somewhat lateral. 



SideroUtes calcitrapoides The Chalk Siderolites. 



Plate X. fig. 1. With four lobes, and punctated through- 

 out. Fossil in the mountain of St. Peter, at Maestricht. 



Genus 16.— DISCO RBIS.—ZawmrcA. 

 Generic Character. — Shell discoid, spiral, multilocular. 



