320 CYPRINID.E. 



coarsely fibrous. The margin is usually, but not always 

 notched ; and as this is the only particular in which the 

 Crassina depressa of Brown appears to differ from 

 Forbes's species, they are probably the same. The 

 name given by Brown is much prior to the other. I 

 believe that in its young state it is the A. crebrilirata of 

 Searles Wood from the Red Crag. 



A. borealis, Chemnitz, which rejoices in the various 

 synonyms of corrugata, arctica, lactea, semisulcata 

 (Leach), islandica, cyprinoides, veneriformis, and com- 

 pressa (Macgillivray), besides several other designations 

 added by palaeontologists, is also a native of high- 

 northern latitudes, but not of our own seas. Imperfect 

 specimens have been dredged in the Hebrides, Moray 

 Firth, and on both sides of Shetland. It is a common 

 newer pliocene fossil, and found in every glacial deposit. 

 The most southern known limit of its habitation is Kiel 

 Bay in the Baltic. The shape of this shell is angular 

 and nearly flat ; the surface is smooth, or faintly striated 

 in the line of growth, except towards the beaks, where 

 there are several fine concentric ribs ; and the epidermis 

 is coarsely fibrous as in A. crebricostata or depressa. 

 It attains a larger size than that shell. The occur- 

 rence of the last two species in our seas, in a semifossil 

 state, may be accounted for in the same way as that of 

 Pecten Islandicus, page 58. 



A. castanea of Say, a North- American shell, has been 

 called British without any sufficient reason. It is the 

 Venus sulcata of Montagu, as well as of Maton and 

 Rackett. Mr. J. Sowerby gave a specimen as " English" 

 to the former ; and Mr. Swainson informed the latter 

 that he received one from the Duchess of Portland, also 

 as "English," and moreover that the shell had since 

 been found in the north of Scotland, where it was known 



