MODIOLARIA. 129 



brown or even pitch-black in .aged examples : margins rounded 

 on all sides except the ventral, which is nearely straight: 

 leaks small, prominent, incurved, and diverging, placed at 

 some distance from the anterior margin : byssal sinus, ligament, 

 and hinge-line as in the other species : hinge-plate strength- 

 ened by a rib to receive the ligament, and finely notched ; 

 ligamental groove narrow and deep : hinge crenulated : inside 

 highly nacreous, purplish -brown, finely notched on the ante- 

 rior and posterior edges, and showing the impressions of the 

 ribs as well as faint traces of similar but finer striae on the 

 middle area : scars distinct. L. 1-5. B. 0*65. 



HABITAT : Muddy gravel, at depths varying from 7 

 to 90 fathoms on the coasts of Yorkshire, Northumber- 

 land, and Durham, both sides of Scotland, and the Shet- 

 land Isles. Although not generally distributed, it is not 

 uncommon in some places, and in the Firth of Forth it is 

 called by the fishermen the " corduroy mussel." The 

 Dogger bank appears to be its southernmost limit in our 

 seas. The Rev. H. W. Crosskey found a single valve in a 

 postglacial bed in the Kyles of Bute. Meyer and Mobius 

 obtained specimens by dredging in the bay of Kiel, on 

 the German coast of the Baltic, whence the species 

 ranges northwards along the Scandinavian shores to 

 Nova Zembla on the east, and Iceland on the west. On 

 the other side of the Atlantic it inhabits the coasts of 

 Greenland, Newfoundland, New England, and Massa- 

 chusetts. 



This fine species may be at once known from M. 

 discors by its sculpture. There are nearly twice as 

 many ribs on the posterior area, and the transverse striae 

 or wrinkles are so coarse as to give a granular appear- 

 ance to that part of the shell. Besides, the anterior 

 margin is more produced, and consequently the beaks 

 recede further from that extremity. The fry are quite 

 smooth and have a prismatic lustre. The largest speci- 

 mens I have seen were lately procured on the Durham 



G5 



