12 CALIFORNIA SEA-SHELLS. 



front of the umbones, is called the lunule. To 

 learn these various parts, compare the following 

 explanation. 



EXPLANATION OF PLATE I. 



Fig. 1, A Univalve ; Purpura crispata. a, 

 apex ; $p, spire ; ap, aperture ; o. I, outer lip ; co,, 

 canal; u, umbilicus; <?, columella ; b. w, body 

 whorl ; Sj suture. 



Fig. 2, A Bivalve, Tapes tenerrima. u, uinbo ; 

 lu, lunule ; a, a, adductor muscular impressions ; 

 j9, pallial line ; p. s, pallial sinus ; I. t, lateral 

 tooth ; , cardinal teeth ; /, ligament 



Moll nsks, like plants, have two names; the 

 first is the generic, or the name of the genus ; 

 the second is the specific, or the name of the 

 species. For example, Myiilus Calif ornianus, 

 the " California mussel." By a species is meant a 

 group of individuals which have such similarities 

 that they may be supposed to have descended 

 from a single pair. A genus is a group of sim- 

 ilar species. The abbreviation after a name des- 

 ignates the author who first gave that name to 

 the species. 



