NIAGARA FALLS AND VICINITY 177 



Class BRACHIOPODA Cuvier 



The Brachiopoda are marine animals, sparingly represented in 

 modern seas, but most prolific in the Paleozoic and early Mesozoic 

 waters. 



The valves of the brachiopod shell are dorsal and ventral, and not 

 right and left as in the lamellibranch Mollusca; they are unequal, 

 and each is symmetric with reference to a median line (longitudinal 

 axis) drawn through its apex. The larger valve may have its beak 

 truncated or furnished with an opening or foramen, for the emission 

 of the fleshy pedicle, by means of which the animal fixes itself to 

 rocks, shells or other substances. 



Certain genera, such as Crania, do not conform to this mode 

 of fixation, but cement their shell directly to the foreign object, 

 while others, e. g. Pholidops, appear to have led a free exist- 

 ence. In many of the discinoid genera, such as Orbicu- 

 1 o i d e a, the pedicle passed through an opening in the lower valve; 

 while in L i n g u 1 a it protruded between the two very nearly equal 

 valves. In all cases the valve giving emission to the pedicle is 

 spoken of as the pedicle valve. 



The opposite valve in the more specialized genera bears on its 

 interior two short processes, or crura, which arise from the hinge 



Fig. SO Diagram of Spirifer. (AB) Longitudinal axis marking the night; (CD) Transverse axis 

 marking the width; (a) Anterior (front) end; (B) posterior (beak) end; (h) hinge line; (ca) cardina 

 area ; (.e) cardinal extremities; (dt) deltidium; (u) umbo; (a) apex or beak 



plate. To these may be attached a calcareous brachidium, which 

 functions as a support for the delicate fleshy " arms ". In a large 

 number of forms this brachidium is absent, and the fleshy arms are 

 directly supported by the crura, but their relation to the valve in 

 question is similar to that obtaining in the brachidium-bearing 

 forms. This valve is designated the brachial valve. In all the 

 forms in which the valves are articulated with each other 

 (Brachiopoda articulata) such articulation is produced 

 by teeth arising from the pedicle valve and lodged in sockets in the 

 brachial valve. The beak of the brachial valve is commonly fur- 

 nished with a more or less pronounced cardinal process, which, at its 



