UNIVALVES. — HALfOTlS. 133 



car, on account of its being much more elongated or dis- 

 tended than any of the other species. 



There are three reasons which operate to create diffi- 

 culty in the arrangement of the different species of this 

 genus: — First, the outside of the shell is generally loaded 

 with marine substances, or else is so much decayed or 

 worn, as not to offer a lineament of the original texture ; 

 thereby precluding all possibility of judgin g by the work 

 or color to what species it appertains. Secondly, as the 

 Ulterior of all Haliotides is enamelled with a magnificent 

 surface of iridescent pearl, no great distinction can be 

 made by a reference to that part of the shell. Thirdly, 

 as the beauty of the shell is considerably increased by 

 being uncoated and polished, so is it also customary to 

 submit it to some such beautifying operation ; which, 

 however, with the surface, at once removes all clue to 

 the attainment of the generic character. 



The exterior of the sea-ears is generally composed of 

 rugae or tuberculations, over which pass approximate ele- 

 vated striae. In some species, foliations supply the place 

 of tuberculations, as is the case in the Haliotis Midae or 

 Midas' ear, the outside of which is wrinkled, and of a 

 dirtyish white complexion; but the inside is of the most 

 beautiful pearl. It grows to eight or nine inches long. 



The back of almost the whole of the Haliotides is fur- 

 nished with a row of orifices near the margin ; their num- 

 ber varies from eight to thirty-eight; and out of that 

 immber from three to seven are generally open, the rest 

 are perfectly closed. There are, however, two exceptions 

 to this general appearance; for the Haliotis imperforata 

 is entirely void of any orifices whatever, as is also the 

 Haliotis perversa, whose spire is turned contrary. The 

 former is deemed one of the great rarities ; its shell is of 



