GLYCIMERIS. 209 



external, behind the beaks. Color ashy white; length 

 from one-fourth to one-half an inch. Found on the 

 roots of kelp, and in similar situations. 



Glycimeris generosa, Gld., Gly-sim/-e-ris gen-e- 

 ro'-sa, Fig. 178. This huge mollusk, which is found 

 chiefly in northern waters, sometimes grows to a lar- 

 ger size than any other bivalve mollusk on our coast. 

 The specimen from which this figure was drawn is 

 over six inches in length, while others are said to be 

 much larger. The valves are oblong and nearly rect- 

 angular, quite flat, and marked with distinct concen- 

 tric ridges. They gape widely where the siphons 

 enter. Ligament external, hinge- tooth on the left 

 valve shaped like a sharp horn, muscle scars very 

 distinct, pallial sinus not very deep. Shells thick 

 and strong; dull white without, pearly and shining 

 within. 



The last family of the Iyamellibranchs is that of 

 the Boring-shells, of which there are two divisions. 

 The first of these includes the Pholadidce or Piddocks, 

 which bore into rock, shell, or clay; the second 

 division, which consists of the Teredos, Teredidcz, 

 work chiefly in wood. 



Of the former division the first species to mention 

 is named Netastomella Darwinii, Sby., Ne-tas-to- 

 mel'-la . Dar-win'-i-i. This little borer is found in 

 rocks. The front of the shell is open and circular; 

 the latter part is prolonged into a narrow, flattened 

 tube, shaped like a duck's bill. The shell is marked 

 with striae, and is divided into two parts by a sudden 

 constriction. Color whitish; length about half an 

 inch. 



Pholas Pacifica, Stearns, Fo'-las Pa-cif'-i-ca. Shell 

 thin and delicate, long and cylindrical; marked with 



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