MYTILUS. MUSSEL. 2 33 
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 Ark low, cn Ireland, is generally attached 
to oysters, v. v* 
11. Mytilus fuscus, Brown Mussel. 
Lister, pi. 359. f. 197 —Brown , JVern. Soc. p. 515. 
“ Shell oblong, narrow, with very tine transverse striae ; 
one side emarginate, the other rounded : beaks prominent, 
carved : minute, and brown.” 
Found at Sligo, and is in the cabinet of Dr. Macdonnell, 
Belfast. 
Listers figure represents it as transversely striate, Mr. 
Dillwyn describes it as smooth. 
12. Mytilus rugosus. Rugged Mussel. 
Lister , pi. 426. f. 267— Pennant , pi. 6*6. f. 1— Donovan, 
pi. 141 —Dorset Cat. pi. 13. f. 5. 
Mytilus lithophogus. 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 the 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 Raekelt, in their report of 
the shells which perforated thestone 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 our native 
rocks; but the former is found in great profusion, mixed 
with theMya dubia, in the range of limestone rocks reach¬ 
ing from Torquay to Plymouth; but more especially in 
l3 those 
