MYTILUS. 



TESTA sequivalvis, obliqua, longitudinalis, sub- 

 cuneiformis, umbonibus antice terminalibus, 

 acutis; latere postico rotundato, (clause ;) basi 

 margineque antico (subhiantulo) lineam conti- 

 nuam obliquam formantibus : ligamento elon- 

 gate, subinterno : impressiones jnusculares duae, 

 postiea majuscula, irregularis, an tica minima, 

 terminalis: impressio museularis pallii irre- 

 gularis, sinu nuUo. 



Shkll equivalve^ obliquely longitudinal, rather wedge- 

 shaped, with the umbones forming a point in front; pos- 

 terior side rounded, not gaping; base forming a continuous 

 line with the anterior margin in an oblique direction to 

 the hinge line : anterior margin very slightly gaping for 

 the passage of the byssus; ligament much elongated, 

 rather internal : muscular impressions two, posterior large 

 and very irregular, anterior very small, terminal; mus- 

 cular impression of the mantle irregular, without any 

 sinus. 



It is well known that the Linn can Genus Mytilus, on 

 account of its principal character being its want of hinge 

 teeth, consists of several forms that are widely distinct 

 from each other, and which have well served as the types 

 of several Lamarckian genera, such as Avicula, Modiola, 

 Anodon, and others in connection with the present Genus, 

 which deservedly retains the name of Mytiliis, both on 

 account of its form, and the priority of its claim. The 

 other genera which have been united with it, but from 

 which it appears necessary to distinguish it because of a 

 certain degree of general resemblance, are Modiola and 



