462 NATURAL HISTORY OF HAWAII. 



that it is smooth and without canals. The outer lip is smooth and sharp. 

 The inner lip is turned back in some species so as to conceal the umbilicus,-'^ 

 as may be plainly seen in one of the species of the genus here shown. The 

 shells, placed in the two hundred and twenty-five or more species in the dif- 

 ferent genera, vary greatly in shape. Examples of the same species often vary 

 through a long series of color patterns, rendering the ten or more species that 

 occur here difficult of determination, even in the hands of specialists and 

 when aided by a large series of shells. 



The living animal is remarkable for the very large foot, which is i;sed to 

 crowd the creature through the sand in search of other moUusks, mostly 

 bivalves, upon which they feed. Their habits are interesting, and as living 

 specimens may occasionally be secured from the sand where their favorite food 

 is abundant, they may be studied to advantage in a small aquarium partly 

 filled with sand and stocked with other living shells. 



Slipper Shells. 



Perhaps the most abundant shells along the coast of our islands are the 

 various species of slipper shells,'''-' cup-and-saucer limpets,^^ the horse-hoof 

 shells ^^ and their allies, all of which are placed in the one family ^^ including 

 the various cap-shaped or limpet-like shells. They usually have a more or less 

 spiral apex, and the interior is often provided with a septum or internal plate 

 of variable shape. 



The living animals are found adhering closely to stones and shells, and as 

 they spend most of their lives in one spot the shell is usually irregularly shaped 

 to fit some particular spot on rock or coral. They feed on the minute 

 free-swimming animals that come their way. In due time they die and add 

 their shells to those light particles of debris cast up at high tide. Represen- 

 tatives of four genera, including the nine or ten species usually found in the 

 islands, are shown. From these the main characteristics for the genera may 

 be determined. 



IIoRSE-IIooF Shells. 



Of the horse-hoof shells, four species occur about Honolulu and Hilo. 

 Hipponyx antiquatus has the apex posterior of the center and is rudely and 

 closely laminated with more or less distinct radial stria?. When alive it has a 

 hairy epidermis. Hipponyx harhahis is more compressed, is strongly radially 

 striated, and has a brown hairy epidermis. Hipponyr imhricatus has the in- 

 terior stained with chestnut. 



Worm Shells and Eulimas. 



Without doubt the most curious of the shell-bearing mollusks are those 

 included in the worm shell family.-** in which tin- twisted .shell might be mis- 

 taken for the tube of some marine worm, as tlii'\' much resemble them iii that 



»^ The name given to the cavity in the centr.il base of the shell when the columella or axis is hollon-. 

 " Crepidiila. '^ Crucibulum. ' '" Hipponyx. ^' CalyptraHila: s* Vermetidw. 



