GASTEROPODA. 89 



peculiar to the Gulf weed. That species is covered with impressed striee, and has a 

 sharp-pointed apex, with more volutions than in the Crag shell. It is possible our 

 shell may be an altered form, having lost its outer coating, and cast off its pointed apex, 

 though its present appearance is much against its identity with the recent one. The 

 recent shell has a more distinct truncation of the columella than is seen in my fossil 

 specimens, where it is more like a plication, or folding over, of the columellar lip, 

 behind which is the small umbilicus. Our shell has an ovate aperture, pointed at the 

 junction of the outer lip with the body whorl, and slightly expanded at the lower part, 

 with a papilliform and glossy apex, without, however, any remains of a roughened 

 edge, which in all probability would have been the case had it ever possessed any 

 greater number of volutions than are now visible. 



ScALARiA,* Lam. 1801. 

 ScALA. Humphries, 1797. 

 SCALARUS. Motitf. 1810. 



AcioNA. Leach, 1815. 

 Clathrus. Oken, 1815. 

 — Ayassiz, 1840. 



Gen. Char. Shell turriculate, with an elevated spire, and generally acute apex, com- 

 posed of rounded volutions, sometimes contiguous, at other times separated ; smooth, 

 transversely striated or decussated, longitudinally costated ; costae generally thin, 

 erect, sharp, and somewhat oblique, often thick and obtuse ; aperture entire, subcircular, 

 rather larger than wide ; peristome continuous, with a prominent and reflected margin ; 

 columella lip slightly everted, forming a subcanaliculated base ; operculum thin, 

 corneous, and spiral. 



The shells composing this genus are of a vitreous texture, of a milky whiteness, semi- 

 transparent, and are in general objects of great delicacy and beauty. They are common 

 through all the tertiaries, and in the recent state are not restricted to any climate, 

 being found in most parts of the world, in the Australian seas, the Indian ocean, and 

 on the coast of Greenland. Some species are still included in this genus that do not 

 possess a vitreous structure, but are opaque shells, and, when better known, may perhaps 

 require to be removed. 



* Etvm. Scala, a ladder. 



12 



