PLATE IV. 



Fig. 1 — Exterior of shell, dorsal view. 



a. p. Anterior portion. lig. Ligament. 



p. p. Posterior portion. 1. v. Left valve, 



d. p. Dorsal portion. r. v. Right valve. 



Fig. 2 — Young shell before leaving the gills. 



v. Valves. by. Byssus. 



h. 1. Hinge-line. c. Cilia, 



a. a. The animal. s. Serrated spines. 



Fig. 3 — Epidermis, 

 p. c. Pigment cells. 



Fig. 4 — Prismatic layer, transverse section. 

 Fig. 5 — Narceous layer, transverse section. 

 Fig. 6 — Section of the shell, 

 ep. Epidermis. nac. Nacreous layer, 



pr. Prismatic layer. 



Fig. 7 — Enlargement of secreting tubes of the liver. 



Fig. 8 — Parasite frequently found on the animal.' 



Fig. 9 — Enlargement of tentacles of the branchial siphon. 



Fig. 10 — Enlargement of muscular fibres. 



Fig. 11 — Mass of the tubules of the liver. 



Fig. 12 — Young Anodonta, 



