PART I. BRIEF DEFINITIONS OF BRACHIOPOD TERMS' 



Adductor muscles (pi. A, figs. 4, 13). — ^The muscles that close the shell. In the Protremata 

 and Telotremata these muscles are inserted in the ventral valve, one on either side of the central 

 axis, between the diductors {q. v.). In passing to the dorsal valve they divide into four, and pro- 

 duce in that shell the two pairs of principal scars known as the anterior and posterior Adductor 



SCARS. 



Adjustor muscles. — Included in the pedicle muscles, q. v. 



Adventitious deposit (pi. A, figs. 7, 10).— Extra fibrous shell substance deposited by the 

 mantle on the inside of the shell, filling up cavities and irregularities of the surface. By deposition 

 of such adventitious shell in the umbonal cavities, the dental plates may be obliterated. 

 Anacline. — See Pt. Ill, Interareas, and t. fig. 1. 



Anterior. — ^That portion of the shell in front of the hinge region, away from the beaks. 

 Apical plate (pi. 23, fig. 9). — A small flat structure situated in the apex of the delthyrium 

 and flush with the interareas. To the under side of it probably was attached the pedicle. This plate 

 is not a relict of the deltidium. 



Apsacline. — See Pt. Ill, Interareas, and t. fig. 1. 

 Area. — See Interarea. 



Articulation. — ^The locking together of the two valves, effected in the main by the teeth of 

 the ventral valve moving in sockets in the dorsal valve, but further assisted by the brachial parts 

 (brachiophores) articulating with the ventral valve, at least in orthoid genera. 

 Brachial valve. — See Dorsal valve. 



Brack idia. — Calcareous brachial supports in the spire- and loop-bearing brachiopods. 

 Brachiophores (pi. A, fig. 7; pi. 4, fig. 29).— Plates that bound the notothyrial cavity (q. v.) 

 in the orthids. More commonly known as socket-plates or brachial apparatus. In a few genera, 

 Brachiophore processes are seen to extend from the distal extremity of the brachiophores, and to 

 them were undoubtedly attached the brachia. The brachiophores may be the homologues of the 

 crural bases of the rhynchonellids, but in any event are more primitive than the latter. 



Brachiophore supports (pi. A, fig. 14j pi. 1 1, fig. 26).— Plates attached to the dorsal face 

 of the brachiophore, and used to strengthen the latter. Known in Hebertella and Schizofhoria. 

 Camera. — See Cella. 



Cardinal angles. — ^Angles formed at each of the extremities of the hinge between it and the 

 forward extension of the shell. 



Cardinal area. — See Interarea and Palintrope. 



Cardinal process (pi. A, figs. 4, 6, 10).— A median unpaired process, lying immediately 

 on the inner side of the dorsal umbo, and serving for the attachment of the diductor muscles. 



Cardinalia. — Processes near the posterior or cardinal margin in the interior of the dorsal 

 valve, connected with articulation, muscle attachment, and attachment of brachial supports. (After 

 Thomson 1927.) 



Catacline. — See Pt. Ill, Interareas, and t. fig. 1. 



Cella (pi. 24, figs. 21, 26). — A small, inverted, V-shaped chamber beneath or ventrad to the 

 ventral median septum of Parenteletes. A similar structure occurs in Dayia, Cyclosfira, and 

 Camarium (Merista). 



Chilidial plates (pi. 16, fig. 22). — Discrete plates, one on either side of the notothyrium, and 

 partially closing it. 



1 For further discussion of many of these terms, see Part III, Morphology. 



