GASTEROPODA. 89 



is peculiar to the Gulf weed. That species is covered with impressed striae, and 

 has a sharp-pointed apex, with more volutions than in the Crag shell. It is pos- 

 sible 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. 



Soalaria,* Lam. 1801. 

 Scala. Humphries, 1797. 

 Scalarus. Montf. 1810. 

 Aciona. Leach, 1815. 

 Clathrus. Oken, 1815. 

 — Agassiz, 1840. 



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

 composed of rounded volutions, sometimes contiguous, at other times separated ; 

 smooth, transversely striated or decussated, longitudinally costated ; costas 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 ; columellar lip slighly 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. 



* Etym. Scala, a ladder. 



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