224 ASTEALIUM. 



Operculum (pi. 60, figs. 42, 43) oval, nucleus submarginal ; out- 

 side white, excavated around the upper edge, with a heavy coarsely 

 grauulose rib following the central part of the spiral, its ends con- 

 nected by a short rib. 



The young are subspinose at the periphery ; adults generally lose 

 the more minute suface-sculpture described above. 



A. c.ELATUM Gmel., 1788. PI. 57, figs. 45, 46. 



Shell conic, solid, imperforate, soiled white, more or less tinged 

 with green and brown ; spii*e elevated, apex acute ; whorls 6-7, 

 convex, with fine incremental strise and oblique radiating folds 

 above ; periphery with several prominent squamose or spinose lirie ; 

 base somewhat flattened, with close squamose lirse separated by 

 deep interstices ; aperture silvery within, transversely ovate, very 

 oblique, its margins fluted ; columella extended, oblique, arcuate. 



Alt. 80, diam. 80 mill. 



West Indies; Bahamas, etc. 



Operculum (pi. 60, fig. 44) oval, nucleus submarginal ; outside 

 convex, white or brown tinted, coarsely granulose. 



This is the Trochus caelatus etc. of Chemnitz, T. ccelatus Chemnitz 

 of authors. 



B. Conic species, with carinated lyeriphery and flattened base. 



In this section of Lithopoma the species are very variable, and it 

 is difficult to find characters salient enough to satisfactorily sepa- 

 rate several of them. Much more material than I have before me 

 must be studied before the synonymy and limits of the various 

 forms can be settled. 



A. AMERicANUM Gmel., 1788. PI. 52, figs. 18-20. 



Shell trochiform, elevated, imperforate, solid, white or yellowish ; 

 Avhorls 7, the upper three smooth in adults by erosion of the sculpt- 

 ure, flattened or concave on their upper surfaces, longitudinally 

 obliquely plicate, the folds numbering about thirty-six on the last 

 whorl, terminating on the periphery in nodules (or spines in the 

 young,) generally intersected about the middle by two to four spiral 

 impressed lines, periphery angled, more or less swollen ; base nearly 

 flat, more or less sharply radiately striate, and spirally lirate, the 

 lirse about six in number, or sometimes more, frequently nodulose ; 

 aperture very oblique ; outer lip usually crenulated ; columella 

 short, heavy, bituberculate at base, bounded by a radiately plicate 

 cordon. Alt. 35, diam. 30-35 mill. 



West Indies ; Florida Keys. 



