LUCINID-iE. 209 



Shell massive, trigonal, ornameutecl with radiating ribs and 

 imbricating foliations ; margins deeply indented ; byssal sinus 

 in each valve large, close to the umbo in front ; hinge teeth I'l, 

 posterior laterals 2-1. 



A pair of valves of T. gigas, weighing upwards of 500 pounds 

 and measuring about two feet across, are used as benitiers in 

 the Church of St. Sulpice, Paris. (Dillwyn.) Captain Cook 

 states that the animal of this species sometimes weighs twenty 

 pounds, and is good eating. 



Axes of great size, weighing seven or eight pounds, are made 

 from the thickest portion of the giant 'j'ridacna by the natives 

 of the Caroline Islands — Dr. J. C. Cox. 



Hippopus, Lamarck, 1799. The " bear's-paw clam " has close 

 valves with two hinge-teeth in each. It is found on the reefs in 

 the Coral Sea. The animal spins a small byssus. H. maculatus, 

 Lam. (cxxviii, 89-90). 



EuRYDESMA, Morris, 1845. 



Distr. — E. cordata, Sowb. Devonian ? N. So. Wales. 



Shell oval or roundly cordate, rather thin, but very much 

 thickened near the beaks, concentrically striated or nearly 

 smooth; beaks strongly incurved, with a sort of an excavated 

 and gaping lunette in front ; ligament large, occupying the 

 greater part of the posterior, more or less straight hinge-area, 

 which is broad and extends below the beaks so as to make the 

 ligament almost internal, one large subconical cardinal tooth in 

 the right valve somewhat curved upward and corresponding to 

 a pit in the left ; several small muscular impressions near the 

 hinge, but no other larger ones perceptible, neither has the 

 pallial impression been as yet traced out. 



(Lucinacea.) 

 Family LUCINIDJE. 



Shell orbicular, free, closed ; hinge-teeth 1 or 2, laterals 1 — 1 

 or obsolete ; interior dull, obliquel}' furrowed ; pallial line simple ; 

 muscular impressions two, elongated, rugose; ligament external 

 or subinternal. 



Animal with mantle-lobes open below, and having one or two 

 siphonal orifices behind; foot elongated, cylindrical, or strap- 

 shaped (ligulate), protruded at the base of the shell; gills one 

 (or two) on each side, large and thick, oval ; mouth and palpi 

 iisually minute. 



The Lucinidffi are distributed chiefly in the tropical and tem- 

 perate seas, upon sandy and muddy bottoms, from the seashore 

 to the greatest habitable depths. The shell consists of two dis- 

 tinct layers. The family first appeared in the Silurian. 



