scHucHEET.] BRACHIOPOD TERMINOLOGY. 75 



Oerontic (Hyatt, emend. Bather andBuckman). — Desig'natingold age. 

 It is indicated in the ontogeny of many species of brachiopods by ex- 

 treme thickness of the valves, obesity, or by numerous, crowded growth 

 hnes near the anterior margin, a condition which sometimes produces 

 truncation and absence of strife at the margin. 



Hinge line. — The line along which articulation takes place. 



Jugum (Hall and Clarke). — The transverse band and its accessory 

 processes uniting the spiralia. When this band is medially incomplete 

 the parts are termed J ugal processes. 



Lateral areas. — That portion of the shell on each side of the ventral 

 axis. 



Listrium (Hall and Clarke). — In some ITeotremata a plate closing the 

 progressive track of the pedicle opening or pedicle cleft, posterior to 

 the apex of the ventral valve. 



Longitudinal axis. — A median line through the shell from the beak 

 to the opposite margin. 



Loop. — The calcareous brachial supports of the Terebratulacea. It 

 is usually composed of descending and ascending lamelLe, united by a 

 transverse band. 



Median septum. — An internal vertical plate commonly developed 

 along the vertical axis and between the muscles of the ventral valve. 

 Sometimes there is also a dorsal median septum. Lateral septa are 

 rarely developed. 



Neanic (Hyatt, emend. Bather and Buckman). — Designating youth- 

 fulness, or the stage in whicli specific characters begin to develop. 



Nepionic (Hyatt). — Designating the smooth-shell stage succeeding the 

 protegulum. 



Pallial sinuses. — Two convergent or divergent iirimary sinuses of tlie 

 circulatory system, traversing the mantle and originating in the poste- 

 rior medial region. They usually have numerous secondary branches, 

 and botli often leave im])ressions in the sliell. 



Pedicle. — The flexible muscular organ of the ventral valve by means 

 of which brachiopods may be attached to extraneous objects. 



Pedicle muscles. — In the Protremata and Telotremata one pair origi- 

 nates on the ventral valve at points just outside and behind the diduc- 

 tors and another on the dorsal valve behind the posterior adductors, 

 while the opposite ends of both are attached to the pedicle. Besides 

 these, there is an unpaired mu.scle lying at tlie base of the pedicle, 

 attaching it closely to the ventral valve. 



Platform. — See Spondylinm. 



Posterior region. — That portion of the shell back of the transverse 

 axis and toward the beak, or apex. 



Primary lamella'. — The primary descending bands of the spiralia, the 

 posterior ends being attached to the crura. 



Prodeltidium (Hall and Clarke restricted). — Tlie third shell plate 

 developed in the earlier embryonic growth of species of Atremata, 



