DEFINITIONS OF BRACHIOPOD TERMS 9 



Lateral plates (pi. A, fig. 11). — External marginal plates restricting the delthyrium and 

 seen only in certain orthids and pentamerids. These discrete plates appear to be formed in exactly 

 the same manner as deltidial plates, q. v. 



Lateral septa. — See Median septum. 



Median ridge. — See Dorsal median ridge, and Median septum. 



Median septum (pi. A, figs. 5, 9). — ^A longitudinal vertical plate between the ventral muscles. 

 Lateral septa are rarely developed between the muscles of the same valve, but are more often 

 present when spondylia are developed. 



Multicostate. — See Cost;e. 



Muscle impressions. — Marks of muscle attachment on the shell, further subdivided as 

 follows: Muscle-scar, a more or less well defined area representing the final or last muscle attach- 

 ment. Muscle-track., the path due to the forward migration of the muscles during growth. 



Myophore (pi. 9, figs. 3, 20; pi. 17, figs. 31, 32). — The rugose surface of muscle attachment 

 on the cardinal process. See Shaft. 



Neanic. — Signifying youth, or the stage in which specific characters begin to develop. 



Nepionic. — Designating the smooth-shell stage succeeding the protegulum. 



NoTOTHYRiAL PLATFORM (pi. 1, fig. 23). — The thickened shell matter in the umbonal interior 

 of the dorsal valve between the brachiophore plates. It is the seat of diductor muscle attachment 

 in primitive brachiopods not yet possessing a cardinal process; in other shells it is the place where 

 the vertical cardinal process arises. This platform has also been called the Pseudocruralium. 



Notothyrium and Notothyrial cavity. — The dorsal counterpart of the ventral delthyrium 

 and delthyrial cavity, q. v. 



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



Palintrope. — The antero-ventrally or antero-dorsally directed shelf developed at the posterior 

 end of the dorsal and ventral valves due to the progressive migration of the hinge margin in its 

 growth. Formerly called cardinal area. 



Pallial sinuses (pi. A, fig. 13). — Extensions of the coelomic cavity into the mantle. Impres- 

 sions of these sinuses are not uncommonly seen on the inside of the shell as low ridges or shallow 

 furrows. There are usually two main trunks in the ventral valve and three in the dorsal. 



PARVICOSTELLiE. See COSTELL^^ 



Paucicostate. — See Cost;e. 



Pedicle callist (pi. A, fig. 13). — A callus of shell substance at the internal apex of the ventral 

 valve between the dental lamellas, to which the postero- ventral surface of the pedicle was attached. 



Pedicle foramen (pi. A, fig. 3). — A small or large round perforation at the apex or elsewhere 

 through the deltidium for the protrusion of a small pedicle; with age, it may become large by abra- 

 sion. When this foramen is absent, the pedicle emerges between the deltidium and chilidium, or 

 these coverings may completely close the delthyrium and notothyrium, in which case there is no 

 known functional pedicle. 



Pedicle muscles. — ^The muscles that retract the pedicle. In the Protremata and Telotremata, 

 one pair originates on the ventral valve at points just outside of and behind the diductors, and 

 another pair on the dorsal valve behind the posterior adductors (not known in orthids), while 

 the opposite ends of both pairs are attached to the pedicle. These muscles are also called the Adjus- 

 tors. (For adjustor scars, see pi. A, figs. 12, 13, 15.) Besides these, there is an unpaired muscle, 

 not known in early brachiopods, lying at the base of the pedicle, attaching it closely to the ventral 

 valve. 



Plane of commissure. — The plane passing through the anterior commissure and the hinge- 

 line. 



Platform. — This term should be retained as first proposed, for the elevated and thickened 

 muscle trace in the trimerellids. See Notothyrial platform. 



