464 NATURAL HISTORY OF HAWAII. 



the beaches of all the islands after a heavy gale. They float on the snrface of 

 the ocean, usually in large companies. They are supported by a raft-like 

 structure formed by a large mass of cells filled with air. All the species recog- 

 nized by Tyron were gathered at Kahana Bay, on Oahu, on the beach on the 

 same collecting trip. The base of the thin shell is always deep violet, while the 

 spire is almost white, tinted with violet. The large violet snail ^-^ is an inch or 

 more in diameter. It is slopingly-convex, is slightly angular on the edge, and 

 has the outer lip very slightly sinous. lanthina glohosa is inflated with a 

 short spire, the whorls are rounded, and the outer lip is slightly more sinuous 

 in the middle. The third species ^"* is much smaller and more conical, the 

 whorls forming an obtuse angle on the outer edge, and there is a deep incision 

 on the outer lip. The species are all said to feed on small surface-swimming 

 animals, especially minute jellyfish. 



Ladder Shells. 



The staircase shells, or ladder shells,*''^ are usually white and polished. The 

 numerous ribs across the whorls are prominent and look like the steps of a 

 ladder, whence they derive their name. They live in the ocean below the low- 

 water mark. They are carnivorous in habit and are fairly common about 

 Hawaii. Ten or more of the many species known, have been reported 

 from the group. The chief characteristics center about their size, the number 

 of whorls and the size and number of the ridges. Scalaria lamellosa, which 

 is representative, has seven or eight whorls, is a fleshy color with a more or less 

 definitely darker band at the suture and above the basal rib. 



Herald's Horn Shells. 



The family CeritJiiidce, a name derived from that given to the principal 

 genus,'*" is represented hy almost fifty species of small shells belonging to four 

 genera. They are all long, many-whorled, spiral shells, with both anterior 

 and posterior canals, and have the lip more or less dentate. They live on the 

 rocks and among the marine vegetation. The species figured "^"^ are found in 

 dredging from Honolulu harbor. They will serve to aid the amateur in plac- 

 ing such shells as may be gathered in the proper family, but the specific char- 

 acteristics for the twenty or more species that may be collected are too minute 

 for consideration here. 



Periwinkles. 



Of the familiar periwinkle ^'^ family two or three species are everywhere 

 abundant on rocky coasts, where they are to be found usually at or above the 

 high-tide mark. They feed on algaj and inhabit brackish and salt water. The 

 species ^^ most common at Waikiki are liesh color or nearly white and have the 

 aperture orange-brown, and may be easily identified as distinct from a spe- 

 cies ^^ common at Pearl Harbor, which is lai'ger. The latter are gray to red- 



** lanthina fragilis. *^ lanthina e.rir/tia. *^ Scalariidft. ^' Cerithiiim = Hpr.ald's horn. 



^* Crrithiiim roliimna and Ceritlnum obcUsciis. *^ Littorinidtv. ^^ Liftorina obesa. 



^^ Littorina srahra. 



