STUDIES IN BIOLOGY. 



THE COMMON MUSSELS. 



(Mytilus latus, edulis, and magellanicus.) 



This paper describes the structure of the above species of Mytilus, 

 and their general characters are given in " The Manual of the New 

 Zealand Mollusca," page 167. The descriptions refer chiefly to 

 M. latus, but frequent comparisons are made where these three 

 species differ. These species are found commonly enough near 

 Dunedin, where my specimens were collected, but they do not seem 

 to range throughout the Islands, except M. latus, which is everywhere 

 common. Professor Hutton (8) states that M. magellanicus and M. 

 edulis are common in the South Island, but not so in the North. 



Shell of M. latus. (Plate II.) 



Shell wedge-shaped, with a slightly prominent angle about the 

 middle of the dorsal side; ventral side prominent in the anterior half * 

 umbones in some specimens very prominent and diverging ; concentric 

 striations more or less evident in the hinder half of the shell. The 

 colour usually serves to distinguish it from M. edulis, as the ventral 

 side of M. latus is generally an olivaceous - brown, or yellow with 

 green towards the posterior margin ; the green colour is seldom 

 altogether obscured, and sometimes in the young is spread over the 

 shell. M. edulis is usually dark blackish- blue. The yellow specimens 

 of young Mytilus, referred to by Professor Hutton (8), I find to be 

 not M. latus, but M. edidis. The shell of M. magellanicus is at once 

 distinguishable from the smoother shells of M. latus and edulis by 

 its longitudinal striations or ribs. In M. latus there is usually one 

 very distinct tooth in each valve at the hinge, and the right valve 

 often shows another smaller upper one. The hinge-teeth in M. edulis 

 are more numerous ; I find several in each valve — not, as given by 

 Professor Hutton, three or four in the left valve and one in the right 

 valve (8). 



