BRACHIOPODA. 147 



No. 688. PanopsBa Faujassi, D'Orb. 



This Lamellibrancli, belonging to the Myacidm, is from the Pliocene Tertiary, 

 Leghorn, Tuscany, and is now in the private Geological Cabinet of Mr. Ward, 

 Eochester. Size, 6x4. Price, $0.80. 



No. 689. Teredina personata, Lam. 



These Pholads (three specimens on pedestal) are from the Eocene Tertiary, 

 Mont Bernon, France. Price, $0.60. 



CLASS V.— BRACHIOPODA. 



These headless Molluscs are inclosed in bivalved shells, which are 

 symmetrical in form, and equal on either side of a vertical line let fall 

 from the beak, while the valves are almost always unequal. The larger 

 one is called the ventral, and the smaller the dorsal. While in the 

 Lamellibranchs, one valve is applied to the right side and the other to 

 the left side of the animal ; in this class, one valve is applied to the 

 back, the other to the belly of the animal. The ventral valve has generally 

 a prominent notched or perforated beak, through which, in most, a pedicle 

 orbyssus passes to attach the animal to some foreign body, for Brachiopods 

 are deprived of the power of locomotion. The one or two accessory pieces 

 occupying a triangular opening under the beak, form an area called the 

 deltidium ; the form and structure, the presence or absence of this, 

 and the muscular impressions, afford good generic characters. The 

 shell structure is so peculiar that a Brachiopod may be deter- 

 mined by the smallest fragment ; it consists of flattened prisms arranged 

 parallel to each other with great regularity. The animal has usually 

 two long spiral prehensile arms developed from the sides of the mouth, 

 and respires solely by the mantle. Brachiopods, of all the Molluscs, 

 enjoy the greatest range in climate, depth and time. They mostly in- 

 habit the deep sea ; so that only 75 living species are known. They are 

 among the oldest of existing forms of animal life. Over 1,200 

 extinct species have been described, distributed through all rocks 

 of marine origin from the Cambrian upwards. They attained 

 their maximum (both of generic and specific developments) in the De- 

 vonian age, and minimum in the upper Oolite. They are the most 

 numerous fossils of the Silurian deposits. The hingeless genera (as 

 Lingula) are most highly developed in the Palseozoic age. Of the 



