Lamarck's Genera of Shells. 245 



granular disc, and the circumference beset with several unequal 

 points, diverging like radii. 



One species. Siderolites calcilrapoides*. 



A small shell, very remarkable for its star-shape ; it is subpa- 

 pillous, with unequal projecting radii, with blunt points. Fossil, 

 Maastricht. PI. vi. Fig. 226. 



3. Polystomellat. 



Shell discoidal, multilocular ; whorls contiguous, not visible ex- 

 ternally ; their surface radiated by transverse furrows or ribs. 

 Aperture composed of several foramina, variously disposed. 



The polystomelke are radiated externally by the projection of the 

 transverse septa of the chambers, which extend from the summit 

 to the circumference of the shell, crossing the whorls, which are 

 not visible on the outside. These characters are common also to 

 the lenticulites, but the aperture of the latter is simple, whilst that 

 of the polystomella is composed of several holes, differently dis- 

 posed in the different species. 



Type. Polystomella crispai. 



No further description. PI. vi. Fig. 227. 4 Species, all recent. 

 4. Vorticialis §. 



Shell discoidal, spiral, multilocular ; whorls contiguous, not 

 visible externally ; septa transverse, imperforate, not extending 

 from the centre to the circumference. Aperture marginal. 



The vorticiales differ from the nummulites chiefly by having a 

 distinct aperture, and from the discorbites, by the spiral whorls not 

 bein» visible externally. Their axis is central, and confounded 

 with the summit of the spire. 



Type. Vorticialis craticulata^. 



No further description. PI. vi. Fig. 228. 

 5. Nummulites ||. 



Shell lenticular, attenuated towards the edges; spire internal, 

 discoidal, multilocular, covered with several thin plates ; exterior 



* Like the rowel of a spur. + From otoXuj, many, and elopa, a mouth, 



♦ Curled. § From vortex, a whirlpool ? 



\ I'Tomcraticuta, a gridiron ? II From nummulux, a small coiu. 



