862 PELEt'YPODA. [Filibranchia. 



Genus 1. MYTILUS (Linne). Bolten, 1798. 



Mytilus, L., Syst. Nat,, ed. 10, 1758, 704 ; Bolten, Mus. Bolten., 1798, 157. 

 Type : M. edulis, L. 



Animal with an elongated linguiform foot ; byssus well developed ; 

 margins of the mantle thick, papillate, fringed posteriorly at the 

 branchial opening, but smooth at the anal orifice ; branchiae nearly 

 equal : labial palpes elongated, free. 



Shell equivalve. cuneiform, very inequilateral ; umbones acute, 

 terminal and anterior ; posterior margin rounded ; cardinal teeth 

 small, or obsolete ; ligament linear, marginal, deep-seated ; interior 

 of the valves commonly lined with nacreous matter ; anterior adductor 

 of the valves small, posterior very large. 



Distribution. Cosmopolitan, the maximum of species in Arctic and 

 Antarctic seas. Abundant and gregarious from high-water mark to a 

 depth of a few fathoms on rocky, stony, or muddy bottom. 



Fossil from the Trias to Tertiary. 



Vernacular Xante. Mussel. 



KEY To SUBGENERA. 



A. Shell smooth. 



a. Hinge with 3 to 5, rarelv only 2 teeth ; anterior adductor- 



scar present ; 2 byssal scars united with the posterior 

 adductor-scar . . . . . . . . . . EUMYTILUS. 



b. Hinge with 1 to 2 teeth ; no anterior adductor-scar ; 



anterior and median byssal scars isolated . . . . CHLOROMYA. 



B. Shell ribbed. Hinge without definite teeth . . . . AULACOMYA. 



Subgen. 1. EUMYTILUS, von Ihering, 1900. 



Kumytilus, von Ihering, P. Mai. S., iv, 1900, 86 ; Jukes-Browne, I.e., vi, 

 1905,217. Type: Mytilus edulis 



Anterior side with a small ribbed expansion under the umbo, the 

 margin of which bears several small teeth, generally from 3 to 5, but 

 sometimes only 2 ; these teeth vary in size and number, even in the 

 same species. Anterior adductor- scar always present, the median and 

 posterior byssal scar united to one another and to that of the posterior 

 adductor. Surface smooth, or concentrically sculptured. 



1. Mytilus edulis, Linne, 1758. Plate 56, fig. \. 



Mi/til us edulis, L., Syst, Nat., ed. 10, 1758. 705 ; Forbes and Hanley, Brit. 

 Moll., ii, 170 ; Conch. Icon., x, f. 33 ; von Ihering, P. Mai. S., iv, 88 ; 

 E. A. Smith, I.e., v, 163; Hutton. M.X.Z.M., 167. M. chorus, Molina : 

 Filhol, Miss. I.C., 544. Hutton, P.L.S. N.S.W., ix, 529 ; not of Molina, 

 M. Dunkeri, Reeve : Hutton, C.M.M., 77 ; J. de Conch., 1878, 52 ; 

 not of Reeve. 



Shell attaining sometimes a large size, oblong-oval or triangular, 

 dilated behind, the beaks anterior and terminal, smooth. Beaks 

 slightly uncinate. close together. Anterior end narrowed, pointed, and 



