Mytilus.} PELECYPODA. 863 



usually somewhat inflated, the dorsal margin ascending on the anterior 

 half, the posterior part broadly rounded or almost straight. Posterior 

 end regularly convex, the basal margin straight or more or less con- 

 cave. Sculpture consisting of fine concentric growth-lines and very 

 fine radiate striae ; under the beaks a small triangular area with 

 prominent ribs corresponding with the hinge-teeth. Epidermis thin, 

 dark olive-brown. Colour deep blackish-blue, sometimes whitish- 

 yellow with brown at the anterior basal part. Interior bluish-white, 

 black outside the pallial line, polished. Margins smooth and sharp. 

 Hinge-plate narrow, oval, with 3 or 4 teeth in each valve, which may 

 be reduced to 2 or 1. Ligament external, long and strong, deep-seated. 

 Adductor-scars 2, the anterior very small, behind the umbo ; the posterior 

 large, roundish, situate at the upper part of posterior end, and confluent 

 with the long and narrow bvssus retractor scar ; the anterior retractor 



^ 



scar of the foot is small, oblong, on the dorsal side behind the beak. 

 Pallial line simple. Byssus consisting of a round stalk, from which 

 on all sides the threads of attachment are given off. 



Diameter. Ant. -post., 50mm. to 120 mm. ; dorso-ventral, 25mm. 

 to 67 mm. : thickness 17. mm. to 40 mm. 



Anatomy. Alex. Purdie, ' Studies in Biology for New Zealand 

 Students," No. 3, 1887. 



Hab. Throughout New Zealand, but more common in the south. 

 Auckland and Campbell Islands. 



The species is abundant around the coasts of the North Atlantic, 

 and in the Mediterranean ; Strait of Magellan to St. Catharina, Brazil, 

 and extending on the west coast of America to California ; Falkland 

 Islands ; Kerguelen Island. It is not recorded from Tasmania and 

 Australia. 



Remarks. Specimens from our subantarctic islands are of a very 

 large size. The animal is used as food and for bait. These mussels, 

 like those of other species, contain sometimes pearls of an inferior 

 quality. 



Fossil in the Pliocene and Pleistocene of Europe and northern parts 

 of America, and in the Miocene and Pliocene of New Zealand. 



Subgen. 2. CHLOROMYA, Morch, 1853. 



Chloromya, Morch, Cat. Conch. Yoldi, pt. 2, 1853, 51 ; von Ihering, P. Mai. S., 

 iv, 87 ; Jukes-Browne, I.e., vi, 218. Type : Mytilus perna, L. 



Umbones more completely terminal, and the anterior side inflexed 

 so as to form a small hinge-plate below the umbo. Shell always 

 smooth. Kiblets of anterior side short, and sharply inflexed beneath 

 umbo. Teeth 1-2 or 2-2 ; most frequently the former, but the single 

 tooth is sometimes in the right, sometimes in the left valve. No 

 anterior adductor-scar ; byssal scars 3 an anterior, a median, and a 

 posterior the latter united to the posterior adductor. 



