60 SCALARIID^. 



are tropical. The West Indian province appears to be the me- 

 tropolis of the genus ; at least more species have been described 

 from that than from any other region. The name indicates a 

 fancied resemblance to a ladder ; in the vernacular the shell is 

 usually known as " Wentle-trap." The synonyms include ScaJa, 

 Klein, 1753; Cyclostoma^ Lam,, 1199, and Sthenorytis, 1868; 

 Gompwpleura and Scalina^ 1865, by Conrad, the three last pro- 

 posed (but not described) for American tertiaiy fossils. 



A number of genera and subgenera have been described, 

 based upon characters of secondary importance, and which can 

 be mostly advantageously reduced to the rank of sections. 



Section Scalaria (sensu stricto). 



Whorls a little separated, crossed b}^ regular lamelliform 

 varices, umbilicated. Aciona^ Leach, 1815, is a synon^'m. 



Section Clathrus, Oken, 1815. 



Shell moderately thick, often colored, whorls united, longi- 

 tudinal ribs usually numerous, aperture suboval, umbilicus 

 covered by the left lip, no basal rib. Janthoscala and Turhona 

 (Brown), Morch, 1876, published without diagnosis, appear to 

 include species of this section. 



Section Opalia, H. and A. Adams, 1853. 



Shell turriculated, imperforate, whorls united, the last with 

 a basal spiral rib. To this group may be referred Psychrosonia, 

 Canefri, 1876, and perhaps Compsopleura (Am. tertiary), Conrad, 

 1865. 

 Section Am.^a, H. and A, Adams, 1853. 



Shell turriculated, thin, whorls united, cancellated, with some 

 thin, irregular varices ; aperture semilunar, inner lip gibbous in 

 the middle, outer lip thin, simi)le. 



Section Cirsotrema, Morch, 1852. 



Shell turriculated, solid, whorls cancellated, with a few irregu- 

 lar, thick, crispate varices ; aperture bordered b^' a thick crenu- 

 lated varix. 



Section Acirsa, Morch, 1857. 



Shell turreted, thin, whorls united, varices obsolete; lip thin, 

 simple. Arctic Seas. 



