THE WHITE STAIRCASE. 49 



marked by strong spiral ridges, winding from the apex 

 to the aperture. 



It is now our pleasant task to consider a few species 

 of pure white shells regularly marked with frequent 

 varices. All of them are quite rare, but if you search 

 along the shore you will probably have the good for- 

 tune to find one or more of them. 



The first one of the group is shown in Fig. 30, and 

 is known as Opalia borealis, Gld., O-pa'- 

 li-a bo-re-a'-lis, or the Northern Opalia. 

 The shell consists almost wholly of the 

 spire, which is composed of about eight 

 whorls, and each of these is crossed by 

 eight blunt ridges. The aperture is entire, 

 and the rounded lips are sometimes stained 

 by the rich purple juices of the animal. 

 The operculum is a brown scale, nearly 

 circular, and showing lines of growth. The color of 

 the shell is white, and its length is about an inch. 



Opalia crenatoides, Cpr., cren-a-toi'-des, is smaller 

 and blunter than borealis. The ridges are less con- 

 spicuous except at the sutures. According to Mr. 

 Carpenter, there are " sutural holes behind the basal 

 rib. 



Fig. 31 is shown the beautiful shell of Scalaria 

 Hindsii, Cpr., Ska-la'-ri-a Hinds'-i-i. It is 

 pure white, very delicate, and is generally 

 less than one inch in length. The whorls 

 are very distinct, finely rounded, and each 

 one is crossed by about twelve thin, sharp 

 Fig. 31. ridges. 

 These shells are so highly prized that they are some- 

 times worn as the drops of ear-rings, while a foreign 

 specimen, the great Chinese Scalaria or Wentle-trap, 



(4) 



