SA XI CAVA. 83 



30 fathoms, 4 or 5 miles off the Deadman in Cornwall ; 

 and a piece of primitive limestone similarly excavated 

 was brought to me by a fisherman, having been hooked 

 up from more than twice that depth about 30 miles 

 eastward of the Whalsev Skerries in Shetland. Vars. 

 1 and 2. Universallv diffused from low-water mark to 

 145 f. (Beechey) . Var. 3. Confined in narrow crevices 

 of rocks, and beneath the hinges of old bivalves. Var. 

 4. In siliceous limestone. This very common species 

 is found everywhere in upper tertiary strata, as far back 

 in time as the Coralline Crag, and it frequently denotes 

 arctic conditions. Glacial formation at Christiania, 

 50-470 feet (Sars) ; Subapennine and Sicilian beds 

 (Brocchi and Philippi); Antwerp (Nyst); newer mio- 

 cene near Antibes (Mace). The extent of its geogra- 

 phical range is almost unparalleled in the history of the 

 Mollnsca. It appears to have spread over the greater 

 part of the globe, from one pole to the other. I cannot 

 distinguish Australian from Greenland specimens by 

 any character except that of size, those from the north 

 being much larger. 



The animal was well described by Fabricius. He said 

 that it was cooked and eaten bv the Greenlanders, and 

 that on being touched or alarmed it squirts out water 

 and contracts itself like an Ascidia. He found the 

 variety pholadis with other shell-fish from deepish water 

 in the crop of the King Eider-duck. The fact of its 

 being byssiferous of course did not escape his notice, 

 and it has been since mentioned by Mr. Osier and Mr. 

 West. It is equally notorious that trias or new-red 

 sandstone (which is not calcareous) as well as limestone, 

 is perforated by the typical form. I can fully corrobo- 

 rate Mr. Clark's observations on this point. Lister 

 noticed nearly two centuries ago that the holes are con- 



