MYTILUS. MUSSEL. 113 



are double the number in M. discors, and is generally of a 

 smaller size. 



In the Firth of Forth it has been found nearly two inches 

 in length ; and at Arklow, in Ireland, is generally attached 

 to oysters, v. v. 



11. Mytilus fuscus. Brown Mussel. 



Lister, pi. 359. f. 197 Brown, Wern. Soc. p. 515. 



" Shell oblong, narrow, with very fine transverse striae ; 

 one side emarginate, the other rounded : beaks prominent, 

 curved : minute, and brown." 



Found at Sligo, and is in the cabinet of Dr. Macdonnell, 

 Belfast. 



Lister's figure represents it as transversely striate, Mr. 

 Dillwyn describes it as smooth. 



12. Mytilus rugosus. Rugged Alussel 



Lister, pi. 426. f. 267 Pennant, pi. 66. f. 1 Donovan, 

 pi. 141 Dorset Cat. pi. 13. f. 5. 



Mytilus lithophagus. Linn. Trans, viii. pi. 6. f. 3, 4. 



Shell oblong, inclining to oval, but varying much in 

 shape, being sometimes kidney-form or approaching to or- 

 bicular, opake, brittle, yellowish-white or rust-color, co- 

 vered with a dull brown skin, rounded at one end, truncate 

 and gaping at th other, transversely wrinkled, with two 

 obsolete angles running from the hinge on the elongated 

 side, one along the cartilage margin, the other obliquely 

 to the front angle, giving the dorsal surface a flattened and 

 somewhat triangular appearance, the ridges of which are 

 frequently armed with a row of small hollow scales : beaks 

 small, near but not close to the rounded end; inside glossy 

 white, thickened under the hinge, with the margin plain : 

 length half an inch ; breadth an inch or more. 



It is evident that Maton and Rackett, in their report of 

 the shells which perforated the stone committed to their elu- 

 cidation by the president of the Linnean Society, have con- 

 founded together the Mytilus rugosus and the M. lithopha- 

 gus. The latter we have not yet discovered in cur native 

 rocks ; but the former is found in great profusion, mixed 

 with the Mya dubia, in the range of limestone rocks reach- 

 ing from Torquay to Plymouth j but more especially in 

 L 3 those 



