BRACHIOPODA. 303 



The pedicle-valve is regularly convex, becoming slightly concave on the 

 cardinal slopes. It bears a moderately broad cardinal area, coextensive with 

 the hinge-line, which is divided by a broad, open delthyrium, which, in no 

 observed condition of growth, bears a covering of any sort, but is filled 

 by the cardinal process of the other valve. The base of the delthyrial 

 cavity is thickened and transversely striated, probably by the attachment 

 of the pedicle-muscle. The teeth are not situated at the extremities of 

 the delthyrial margins, but lie within and in front of them, arise from 

 the bottom of the valve as two erect, divergent subquadrate crests, rest- 

 ing upon low ridges which bound the muscular area. These peculiar teeth 

 are smooth and abrupt on their inner faces, while their outer faces are 

 deeply crenulated. A low groove separates each from the cardinal area. 

 The muscular area is broadly flabellate, extending more than half-way across 

 the valve, and consists of two large diductor scars enclosing a narrow median 

 pair of adductors. 



The brachial valve is slightly concave, often nearly flat. Cardinal area nar- 

 row, but clearly developed; chilidium prominent. Cardinal process large, erect, 

 smooth on its posterior surface, and bilobed at its summit. Each of these lobes 

 is excavated above, so that the upper portion of the posterior wall is free from 

 the rest of the process. In front of this is a broad, smooth floor, sloping 

 toward the bottom of the valve. The margins of this area form the elevated 

 socket-walls, and their anterior extremities are the bases of the crura. The 

 dental sockets are deep and their outer walls corrugated for the reception of 

 the teeth. The posterior portion of the sockets and the lower part of the 

 cardinal process are covered by the erect, convex chilidium. At the anterior 

 edge of the cardinal process lies a broad, thick, not elevated median ridge, 

 which gradually narrows and becomes developed into a sharp, thin septum, 

 attaining its highest point at about the center of the valve, whence it slopes 

 rather more abruptly downward, terminating at the anterior third of the valve. 

 From the crural bases extends a pair of long, slender lamellar processes, which 

 curve outward, are directed upward, again converge and unite with the median 

 septum on its lateral faces and just in front of its highest point. Slightly con- 



