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; sp, spire; ap , aperture ; o. I, outer lip ; ca\ 
canal; u, umbilicus; c, columella; b. w, body 
whorl ; s, suture. 
Fig. 2, A Bivalve, Tapes tenerrima. u, umbo ; 
lu , lunule ; a , adductor muscular impressions ; 
p , pallial line ; p. s , pallial sinus ; l. t , lateral 
tooth ; cardinal teeth ; Z, ligament 
Mollusks, 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, Mytilus Calif or nianus, 
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. 
