The Furbelowed Clams 



I 



of these shells, whose hardness is remarkable. So far has the 

 process of calcification proceeded that scarcely a trace of animal 

 matter remains in an adult shell. Out of the open lunule (the 

 depression in front of the hinge) the foot projects and from 

 the gland a powerful tendinous byssal cord is spun. By this 

 the mollusk is anchored to coral rocks. 



T. gigas is distinguished at any stage of its growth by the 

 four broad, main ribs, set with many close, short scales, which 

 become still shorter as age advances. The shell veers obliquely 

 forward in growth, which makes it unsymmetrical. The lining 

 is tinged with rose. Diameter, 2 to 3 feet. 



Habitat. — Indian and Pacific Oceans. 



The Serrated Tridacna (T. serrifera. Lam.) has the sym- 

 metry of T. squamosa, and the few broad ribs of T. gigas; but the 

 scales are reduced to lines of sharpened points following the ribs 

 out but a short way from the umbones, and always more distinct 

 on the anterior region. The whole surface is crossed by stria- 

 tions, radiating and concentric, which are stronger in the broad 

 interstices than on tfie ridges. The white surface has a yellow 

 tinge. Diameter, 3 to 4 inches. 



Habitat. — Moluccas. 



Three smaller species occur in the Philippines, all obliquely 

 elongated, and well ruffled, so that one can know them at a glance 

 as belonging to the genus. 



THE BEAR'S PAW CLAM 

 Genus HIPPOPUS, Lam. 



Shell massive, equivalve, regular; hinge with two teeth in each 

 valve; lunule nearly closed; sculpture of elaborate frilled scales 

 on its numerous ridges and interstices. Single species. 



The Spotted Bear's Paw Clam (H. maculatus, Lam.) is 

 one of the most elegant and highly prized of bivalve shells. Speci- 

 mens are obtained in great abundance from eastern seas and 

 distributed all over the world. Yet never a second species, nor 

 even a distinct variety has been found, though the type species has 

 been well known for nearly two centuries. The gracefully curved 

 ridges and intervening sulci are adorned with rows of frond-like 



364 



