CHAMA, CARDIUM AND VENUS 71 



valves are often torn off by the waves and washed 

 ashore. They are easily identified, though a novice 

 often confounds them with limpet-shells. I have 

 some exceedingl)^ beautiful specimens that were 

 taken from piles that had been pulled up from a 

 disused wharf at San Pedro. 



Chama exogyra, Conr., the Reversed Chama, has 

 a coarser, more opaque shell, with but little beauty 

 of form or color, and is usually of a dirty white 

 color. The chief difference, however, is determined 

 by the curve of the umbones. If you stand a speci- 

 men of this species on its edge, with the beaks upper- 

 most and curving towards you, the side which was 

 attached to the rock will be towards your left hand. 

 But if you place a specimen of pellucid a in the same 

 position, the rocky side will be towards your right 

 hand. I have gathered the two species growing side 

 by side, and I have never known this rule to fail. 

 Both of these species live at Monterey. 



Chama spinosa^ Sby., the Spiny Chama, is a south- 

 ern species, living mostly along the Mexican coast, 

 but perhaps reaching as far north as San Diego. It 

 resembles the first species, but its ridges are broken 

 into close, short spines. 



We now come to the interesting family of the 

 Heart-shells, or Cockles, as they are called in many 

 places. There are over two hundred species of them 

 known in different parts of the world, and they vary 

 exceedingly in size and appearance. They are all 

 very decidedly heart-shaped, whether you look at 

 them from the front or the back of the shell. Most 

 of them have prominent ribs running from the umbo 



