TERMINOLOGY. 295 



Pedicle opening. — See Delthyrium. 



Pedicle tube. — See Foranunal tube. 



Platform. — An internal median thickening of the shell elevating the muscles. Seen in cer- 

 tain families of the Atremata and more rarely in the Neotremata. (See Spondylium and pp. 307 

 and 309.) 



Pleurocceles. — ^Areas between the parietal band and the outer posterolateral margins. 

 (After Kmg.) 



Posterior region. — That portion of the shell back of the transverse axis and toward the 

 beak or apex. 



Protegulum. — ^The initial shell of brachiopods. It is smooth and of microscopic size, in 

 outline being semicircular or arcuate and without cardinal areas. 



Protractor muscles. — See' Outside and middle lateral muscles. 



Protremata. — ^Articulate calcareous brachiopods with the pedicle opening restricted to the 

 ventral valve throughout life or during early growth. Pedicle aperture modified by the del- 

 tidium. Brachia unsupported by a calcareous skeleton but nearly always by a crura of 

 variable length. For a more detailed description see "Classification of Cambrian Brachiop- 

 oda," page 325. 



Pseudo-area. — See Cardinal area. 



Pseudochilidium. — See Cliihdium. 



Pseudocruralium. — Dorsal equivalem; of pseudospondylium. 



Pseudodeltidium. — The convex medial portion continuous with the ventral cardinal areas 

 in Atremata and Neotremata. (See Deltidium.) 



Pseudopedicle groove. — See Pedicle groove. 



Pseudospondylium. — See Spondylium. 



Retractor muscles. — See Anterior lateral muscles. 



Septal plates. — Plates supporting the crural processes, also known as crural plates. (See p. 3 10.) 



Sessile spondylium = Pseudospondylium. 



Splanclmoccde. — The area within the parietal band. (After King.) 



Spondylium. — ^A plate in some articulate brachiopods, mainly the Pentameracea, formed 

 by the union of converging dental plates, to the upper surface of which are attached the adduc- 

 tor, diductor, and pedicle muscles. The spondylium maj^ rest upon the ventral valve or may 

 be supported by a median septum. The spondjdium appears to be first indicated in the artic- 

 ulates by a thickening of the shell of the ventral valve beneath the umbonal region so as to 

 form an area upon which all the muscles of the valve have their points of attachment. In 

 Billingsella this is beautifully illustrated by B. exporrecta (PL LXXXVIII, figs. Id, le, and 2a) and 

 B. plicatella (PI, LXXXVI, figs. 3i, 3k, and 3m). In its development the spondyhum is fore- 

 shadowed in the Atremata by the so-called platform of Elkania (PL LI, figs. 1 and la) and by the 

 still more primitive form in Obolus (PL VI). For the purpose of reference the rudimentary spon- 

 dylia attached directly to the inner surface of the valve, sls in Billingsella, laaj he called pseudo- 

 spondylia (sessile spondyHa, Ulrich) , and those free or supported by a septum or septa, spondylia. 

 In the Atremata the homologous equivalent has been known as the platform. In Obolus, 

 Elkania, etc., there is sometimes developed in the dorsal valve a plate similar in appearance 

 to the spondylium, but different in origin; this is known as the cruralium. (See p. 307.) 



Teetli. — Two processes of the ventral valve of articulate brachiopods, serving for articula- 

 tion. (See p. 307.) 



Telotremata. — Articulate Brachiopoda with the pedicle opening shared by both valves 

 in nepionic and early neanic stages, usually confined to one valve in later stages, and becoming 

 more or less modified by deltidial plates in ephebic stages. Brachia supported by calcareous 

 crura, loops, or spiraUa. Prodeltidium absent. (After Schuchert.) 



Transmedian (rotator) muscles. — In the Obolacea these are situated posteriorly just in 

 advance of the umbonal muscle, two on one side and one on the other. By their contraction 

 the dorsal valve turns alternately, first in one direction and then in the other. 



Transverse axis. — A line through the shell from right to left midway between the beak 

 and anterior margin. (See Longitudinal axis.) 



