A Lamellibranch. 53 



A LAMELLIBRANCH 



( Venus mercenarid). 



External Anatomy. The shell is composed of two 

 bilateral halves or valves ; the hinge, or their common line 

 of union, marking the dorsal side. The anterior end is 

 less elongated than the posterior. The iimbo is the dome- 

 shaped elevation along the dorsal edge of each valve. Lying 

 dorsally, between the valves, and extending posteriorly, is the 

 ligament. Which is the right valve, and which the left? 

 Note the parallel lines of growth. 



Draw. 



Pry the shells apart and note the thickened mantle- 

 edge, running parallel to the free margin of the shell. 

 It is partly divided into a right and a left half, by lon- 

 gitudinal openings. The anterior and ventral opening 

 {pedal} gives opportunity for the protrusion of the foot 

 while the posterior or siphonal permits the ingress and 

 egress of salt water. 



Internal Anatomy. Remove the left valve of the shell, 

 taking care not to injure any of the underlying soft parts. If 

 the animal has been killed by being allowed to stand in 

 warm fresh water for a little time, the valves will naturally 

 gape apart, and the attachments of the strong adductor 

 muscles may be pressed from the shell with the handle of 



