MANUAL OF NATURAL HISTORY. 137 



a lateral fringe ; head-lobes developed ; shell 

 turbinate, pearly within ; operculum calca- 

 reous. 



2. Family.— Top-Shells (Trochidae). Foot with a 



lateral fringe ; head-lobes rudimentary ; shell 

 conical, spiral, pearly within ; operculum 

 horny. 



3. Family. — False-Ears (Stomatellidse). Foot with 



a lateral fringe ; front edge of mantle entire ; 

 muscular impression crescentic ; shell ear- 

 shaped, imperforate, pearly within ; opercu- 

 lum none or rudimentary. 



4. Family. — Sea-Ears (Haliotidae). Foot with a 



lateral fringe ; head-lobes developed ; mantle 

 with the front edge fissured ; muscle of at- 

 tachment oval, central ; shell ear - shaped, 

 pearly within, with a series of holes ; oper- 

 culum none. 



5. Family. — Nerites (Neritidse). Foot simple, with- 



out a lateral fringe ; head-lobes none ; shell 

 spiral, turbinate, not pearly within; oper- 

 culum sub-spiral, calcareous, with an internal 

 process. 



II. SUB-ORDER. — Sessile-eyed Scutibranchs 

 (Edriophthalmata). 



Eyes sessile, or on a slightly-raised tubercle on 

 outer side of base of tentacles ; shell (adult) symme- 

 trical, conical, not spiral, not pearly within ; oper- 

 culum none. 



