224 



THE SEA SHORE 



the Brachiopods, at one time very abundant, as proved by the 

 immense number of fossil shells embedded in various stratified 

 rocks, but now represented by only a few living species. 



The shells of these animals are commonly known as Lamp 

 Shells, on account of their resemblance to an antique lamp ; and 

 although at first sight they bear a general likeness to certain bivalve 

 shells of lamellibranchs, a close examination will show that not 

 only the shell, but also the animal residing within it, are both of 

 a nature very different from that of the molluscs with which they 

 were at one time supposed to be closely related. 



The valves of the shell are unequal, 

 and are not placed respectively on the 

 right and left sides of the body of the 

 animal, but rather on the dorsal and 

 ventral or upper and lower sides. The 

 ventral shell is the larger, and is pro- 

 duced into a beak which sometimes has 

 a round hole corresponding in position 

 with the hole for the wick of an antique 

 lamp, and the dorsal or smaller valve 

 is always imperforate. The hinge is a 

 perfect one, the junction of the two 

 valves being so well secured by it that 

 it is impossible to separate them without 

 injury. It is formed by two curved teeth 

 on the margin of the ventral valve that 

 fit into corresponding sockets on the 

 dorsal. A few brachiopods, however, 



have no hinge, the valves being secured by means of numerous 

 muscles. The hole in the shell serves for the protrusion of a 

 pedicel or foot by means of which the animal is enabled to attach 

 itself. 



Two long arms, covered with vibratile cilia, and capable of 

 being folded or coiled, are attached at the sides of the mouth. They 

 are practically processes of the lips, mounted on muscular stalks, 

 and attached to a delicate calcareous loop on the dorsal valve ; and 

 serve not only to produce water currents for the conveyance of 

 food to the mouth, but also answer the purpose of gills. 



The digestive system of a brachiopod includes an resophagus 

 that leads into a simply formed stomach round which is a large 

 digestive gland. The heart has only one cavity, but the animal 



FIG. 154. Terebratulina. 

 THE UPPER FIGURE RE- 

 PRESENTS THE INTERIOR 

 OF THE DORSAL VALVE 



