The Wing Shells, Pearl Oysters and Hammer Oysters 



When ready to descend, the diver sHps over the side of the 

 boat, holding to the rail with one hand and holding the water 

 glass in the other. Locating some particular point at the bot- 

 tom, he lets go of the rail, drops the glass, takes a deep breath 

 and sinks out of sight, feet foremost. Descending about ten feet, 

 he quickly turns head downward, and swims to the bottom. 

 When hardly a third of the distance has been reached, he has the 

 appearance of being on the bottom, so transparent is the water. 

 On reaching it he places himself in a horizontal position, seemingly 

 hauling himself along from one point to another. 



One man consented to give an exhibition dive in deep water. 

 The cutter was dropped off a short distance from the shoal, and 

 a sounding made in seventeen fathoms (102 feet) of water. We 

 watched through water glasses the diver's movements from the 

 time of sinking below the surface until rising to the top again, 

 two minutes and forty seconds. 



Reaching his destination, he began picking over pieces of 

 coral, brushing aside broken shell and other debris in the same 

 manner as if he were working in a garden. He investigated the 

 bottom for some sixty or seventy feet from -the initial point of 

 landing. When ready to ascend he stood erect, and came up 

 as if being pulled with considerable force, shooting out of the 

 water half-way to the waist. He seemed to suffer no unusual 

 discomfort, and in a short time was ready to go down again. 

 There is a record dive of twenty-three fathoms. 



THE PERNAS 

 Genus PERNA, Brug. 



Shell nearly equivalve, squarish, flattened, right valve with 

 byssal sinus; hinge broad, crossed by a series of ligamental grooves; 

 umbones small, often terminal and hooked. A small genus with 

 variable forms in tropical seas, chiefly eastern. 



The Saddle Perna (P. ephippium, Linn.) is well named 

 from its general outline. The coppery-red surface is covered 

 with wavy laminations that seem to have fused and become 

 obsolete. The anterior end has a deep concavity. The umbones 

 form a hook. Diameter, 4 to 5 inches. 



Habitat. — Honduras. 



The Purse Perna (P. marsupium, Lam.) has much the 

 same form as the pearl oyster. It is a small species from the 

 Philippines. 



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