104 MYTILIM. 



mined the beaks in a common mussel must see that 

 they are not placed at the end. Their comparative 

 distance from this point is in every case, whether of 

 Mytilus or Modiola, a mere question of degree. The 

 so-called Modiola are invariably fixed by a byssus ; and 

 the typical species (M. modiolus) are attached to the beds 

 on which they congregate precisely in the same way as 

 Mytilus edulis. The only appreciable difference in a 

 generic point of view that I can detect between M. mo- 

 diolus and M. edulis is that in the latter the front 

 edges of the mantle are fringed, while in the former they 

 are plain, and also that the small tubercles of the hinge 

 in M. edulis only occur in the very young of M. modiolus, 

 and not in a subsequent stage of growth. In M. pha~ 

 seolinus, however (which has always been regarded as a 

 Modiola), these tubercles are represented by minute 

 but distinct crenulations. The shells of all the British 

 species of Mytilus are smooth. The byssus proceeds 

 from a gristly shaft, which appears to support the bundle 

 of filaments like the handle of a broom. Mytilus is a 

 very ancient name, and was also spelt by classic authors 

 Mytulus, Mitulus, and Mutulus. The animal is the Cal- 

 litriche of Poli. 



1. Mytilus edulis"^, Linne. 



M. edulis, Linn. Syst. Nat. p. 1157 ; F. & H. ii. p. 170, pi. xlviii. f. 1-4, 

 and (animal) pi. Q. f. 5. 



Body varying in colour from white to orange-yellow, with 

 a tint of reddish-brown or purple : mantle having two mar- 

 gins ; outer one plain ; the inner one pinnated, or fringed on 

 the ventral and anterior sides with 15-25 tentacular cirri, and 

 serrated on the branchial portion : foot dark brown, occasion- 

 ally streaked with w r hite down the middle. 



Shell irregularly triangular, expanding from the smaller 



* Eatable. 



