THRACIA. 223 



mantle closed throughout, except quite anteriorly, where 

 there is a fissure for the passage of a compressed, not very 

 large linguiform foot ; and posteriorly for the issue of two 

 large rather long tubes, which are separate nearly their 

 whole length, and divergent at their extremities, which 

 have each a few rays. The branchia) consist of only one 

 lobe on each side, which has a longitudinal furrow in the 

 middle, and is reflected for half its height, on the inner 

 surface, precisely in a similar manner with that described 

 as occurring in Lyonsia Norvegica. There are on each 

 side the branchial lobes two small triangular labia. The 

 animal is of a white colour throughout." — Clark MSS. 



This is by far the most abundant of our Thracias^ being 

 a tolerably plentiful bivalve, and one that is widely diffused. 

 It is taken in Northumberland (Alder) ; Scarborough 

 (Bean); Weymouth (S. H.); various spots in S. Devon 

 (Jeffreys) ; and on the sandy shores of both eastern and 

 western coasts, from Cornwall to the Shetland Islands 

 (M' Andrew). A variety is met with at Plymouth, in 

 which the length is twice and a half the breadth (Jeffreys 

 cab.). At Tenby it is peculiarly abundant (S. H.), and is 

 likewise procured at Swansea, and the neighbouring coves 

 (Jeffreys). Among its Irish localities we may specify 

 Belfast, Strangford, Dublin, and Bantry Bays (Thompson), 

 and Cork Harbour (Humphreys). It has a wide range in 

 depth, having been taken alive in five fathoms at Unst, 

 and dead in thirty, seventy, and a hundred fathoms, 

 around the Shetland Isles, sometimes more than twenty 

 miles from land. Lieut. Thomas has dredged it in twenty- 

 seven fathoms off the coast of Northumberland. 



This species ranges from the coasts of Norway to the 

 Levant. It is the most ancient of our Thracias^ being 

 found fossil in the coralline crag. 



