MYTILUS. 115 



f 



side incurved, and dorsal side arched instead of being angu- 

 lated. 



Monstr. Upper valve nearly flat and much smaller than the 

 other. 



Habitat : Not uncommon on the southern and west- 

 ern coasts of England, Wales, and Ireland, and found 

 by Mr. Bean at Scarborough, on rocky and stony ground, 

 from low-water mark to 18 fathoms. Var. Portsmouth 

 (J. G. J.). Monstr. South Devon (Mus. Loscombe). 

 This species is a Red Crag fossil. It has not been re- 

 corded from any place north of England; but its south- 

 ern range extends to the iEgean and Algeria. 



According to Mr. Clark the gills " entirely coast the 

 body, being brought close to the posterior extremity to 

 receive the water. This structure of the branchiae is 

 the substitute for the absence of tubes or any sort of 

 siphonal fold of the mantle." The shaggy beard of the 

 shell is very peculiar. Montagu says that it is partly 

 owing to the epidermis being broken and divided into 

 fibres; and he also observes that, while in a soft and 

 glutinous state, it arrests such extraneous matter as 

 comes in contact. Gould suspected that the epidermis 

 was a parasitic vegetable ; but he evidently had not then 

 had an opportunity of seeing it. The byssus resembles 

 a bundle of fine tow. M . barbatus differs from the young 

 of M. modiolus in the shell being narrower at the an- 

 terior and much broader in proportion at the posterior, 

 side, as well as in the angularity of the dorsal margin, 

 straight hinge-line, strong laminar ridges, reddish colour, 

 and the epidermis being serrated or barbed on one side 

 instead of being plain as in that species. 



This species does not appear to inhabit the north of 

 Europe, unless it is the shell noticed by Muller in his 

 ' Zoologia Danica • as smaller than M. modiolus, with a 



