CONCHIFERA. 49 



the pointed end sunk deeply into the mud. The 

 Mussel associates in dense beds on rocks between 

 tide-marks. The little Crenelles crawl about bushy 

 sea-weeds, by means of their long foot. The Mo- 

 dioli and the Area hide in crevices of rocks, and 

 under stones. The Cockles, the Venerida, the 

 Maetradae, the Donacida, the TelKnada, the Eazors 

 (Solenid&\ and the Gapers (Myadae), all burrow 

 into mud or sand, from the level of the tide to 

 great depths. The Gastrochaenadce and the Pho- 

 ladidae bore into stone and other substances, and 

 the dreaded Ship-worm (Teredo) into submerged 

 timber. 



Identification. Mr. S. P. Woodward enume- 

 rates, as " characters which have been most relied 

 on for distinguishing" the families and genera of 

 Conchifera, the following, stated nearly in the order 

 of their value : 



" The extent to which the mantle-lobes are 

 united ; the number and position of muscular im- 

 pressions ; the presence or absence of a pallial 

 sinus; the form of the foot ; the structure of the 

 gills ; the microscopic structure of the shell ; the 

 position of the ligament, internal or external ; the 

 dentition [toothing] of the hinge ; equality or 

 inequality of the valves ; regularity or irregularity 

 of form ; the habit, whether free, burrowing, or 

 fixed ; the medium of respiration, whether fresh 

 or salt water. "* 



Authorities. For structure, I have been much 

 indebted to Siebold's " Comparative Anatomy of 

 the Invertebrate ; " for systematic arrangement, 

 I have consulted Forbes and Hanley's elaborate 



* Manual of the Mollusca, 253. 

 E 



