CHAPTER XXVIII: THE STAIRCASE SHELLS. 

 LADDER SHELLS. WENTLETRAPS 



Family Scaliid^ 



Shell white, polished, turreted; whorls sometimes uncoiled, 

 with longitudinal ribs bearing prominent plates; aperture round; 

 operculum spiral, horny. Head has retractile proboscis; tenta- 

 cles close together, with eyes at their bases; jaws toothed or spiny; 

 radula elaborate. Sexes distinct. A creeping, carnivorous 

 family of world-wide distribution, allied to lanthinidas. 



Genus SCALA, Humph. 



Characters of the family. Living species, 200; fossil species, 

 200. 



The peculiar flanges that decorate these shells, making them 

 resemble spiral staircases, are the successive limits of periods 

 of growth. Each in turn has been the shell's lip until growth 

 began again, and it was left behind. The genus has a wide 

 distribution from arctic to tropical seas in eastern and western 

 hemispheres, from low water mark to abyssmal depths. The 

 West Indies have furnished the greatest number of species. 

 Large species measure 2^2 inches in length; one species, 4 to 5 

 inches. When disturbed, the wentletraps exude a purplish fluid. 



The Precious Wentletrap {S. pretiosa, Lam.) has had a 

 romantic history. It was long considered a Chinese shell, but 

 was later found also oflf the Australian coast and among the 

 Moluccas. It is one of the largest known species, reaching 2^ 

 inches in length. It has a broad-based spire of eight roundish 

 whorls, smooth and white, decorated with ivory white flanges 

 or ribs that cross the whorls at regular intervals. The sutures 

 are deep and the umbilicus wide. The mantle has a flaring rim. 



About the year 1700 these shells attained an exorbitant and 

 fictitious value in the estimation of shell collectors. Forty guineas 

 (I200) was paid for a single specimen. Fifty years later this price 



157 



