NO. 5 RHYNCHONELLOID BRACHIOPODS — COOPER 55 



the obscurely costellate surface, the rectimarginate anterior com- 

 missure, and the disjunct deltidial plates. In most specimens the 

 median portion of one or both valves is marked by a depressed line or 

 flattening that produces an emargination of the anterior. The deltidial 

 plates are usually strongly developed but have not been observed to 

 meet. 



In the apex of the pedicle valve a small triangular plate appears 

 which is elevated above the valve floor. This forms a partial sheath 

 for the pedicle which rests against it. The teeth, as in most modern 

 rhynchonelloids, are corrugated and are supported by well-developed, 

 erect dental plates defined by deep umbonal cavities. The muscle 

 field is small, with a large subquadrate flabellate diductor field sur- 

 rounding the adductors anteriorly. The adjustor scars are small and 

 are located just anterior to the front of the dental plates. Faint 

 pallial marks preserved in one specimen show the vascula media 

 as in Hispanirhynchia. 



The most interesting parts of Frieleia are the cardinalia. The 

 diductor muscles are attached in a small, triangular, horizontally 

 striated pit at the apex. In some specimens this is much thickened to 

 form a cardinal callus. The socket ridges are strong and curved. To 

 them are attached small triangular outer hinge plates. The hinge 

 plates bear the crural bases and crura. The crural bases are further 

 strengthened by inner hinge plates that extend dorsally to unite with 

 the median septum to form a small chamber. I am unable to detect 

 any substantial resemblance of this structure to that of Camarotoechia 

 or even to the camerate Mesozoic rhynchonelloids. 



The median septum in Frieleia is a narrow, strong, elevated plate 

 that is a myophragm and a crural buttress. It is interesting to note 

 that the inner hinge plates, in decking over the space between the 

 crural bases, do not form a septal chamber as in Camarotoechia but 

 fill in the space solid. In some specimens the inner hinge plates coa- 

 lesce in such a way as to form an undivided but concave hinge plate. 



The adductor field is divided by the median septum and is long and 

 slender. The anterior scars are elongate, tear shaped in outline. The 

 posterior pair is smaller and lies posterolateral to the anterior pair. 



Frieleia has not yet been definitely identified in the Tertiary of 

 California or Japan. It has distinctive characters and is one of the 

 few modern or Tertiary brachiopods having a prominent median 

 septum. Several species occurring on the Pacific Coast of the United 

 States may be referable to Frieleia, especially if the definition were 

 to be broadened to some extent. The so-called Hemithyris astoriana 



