201 



RADIOLATA.— Three Genera. 



Shell discoidal, spire central, chambers elongated, radiated, extending from 

 the centre to the circumference. 



Rotatiles. Shell orbicular, spiral, convex or conoidal above, flattened or 

 radiated and tuberculated beneath, multilocular; aperture marginal, triangular. 



A fossil. 



Lenticulites. Shell sublenticular, spiral, multilocular; the external 

 margin of the whorls folded in two, extending above and below, even with 

 the centre of the shell; septa entire, curved, the two sides prolonged in the 

 form of rays; aperture narrow, projecting over the penultimate whorl. 



A fossil. 



Placentula. Shell orbicular, convex above and beneath, multilocular; 

 aperture oblong, narrow, formed like a ray on the lower, or on both discs. 



A minute nautilus of Fichtel, Ency. Meth. pi. 466, fig. 9. a. b. c. d. 



NAUTILACEA.— Six Genera. 



Shell discoidal, spire central, the chambers short, not extending from the 

 centre to the circumference. 



Discorbites. Shell discoidal, spiral, multilocular, sides simple; the 

 whole of the whorls apparent, naked, and contiguous to one another; septa 

 transverse, frequent, not perforated. 



A fossil. 



Siderolites. Shell multilocular, discoidal; whorls contiguous, not ap- 

 parent outside; disc convex on both sides, and studded with tubercles, with 

 unequal and radiated lobes on the periphery; septa transverse and imperfo- 

 rate; aperture distinct and sublateral. 



A fossil. 



Polystomella. Shell discoidal, multilocular; whorls contiguous, not 

 visible externally; the exterior radiated by transverse furrows or ribs; aper- 

 ture composed of many holes, variously disposed. 



A minute nautilus of Fichtel. 

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