54 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



Elongate oval to subtriangular in outline, with the greatest width 

 at or anterior to the middle; thin shelled; inequivalved, the pedicle 

 valve having the greater depth and convexity; rectimarginate to 

 ligate ; surface smooth to obscurely and minutely costellate. Beak of 

 pedicle valve short, nearly straight to suberect; foramen incomplete, 

 elongate oval, hypothyrid; deltidial plates thick, disjunct but nearly 

 united; apex marked by a small triangular plate elevated above the 

 valve floor. 



Pedicle valve interior with long, curved, corrugated teeth buttressed 

 by prominent and strong dental plates; muscle and pallial marks 

 lightly impressed ; diductor field subquadrate, small, surrounding 

 adductors ; vascula media branching at about midvalve, the branches 

 diverging anteromedially and anterolaterally. 



Brachial valve interior with deep corrugated sockets margined by 

 thick overhanging socket ridges ; crura, of spinulifer type, thin, long, 

 divergent, attached directly to the socket ridges ; inner hinge plates 

 small, rounded, disjunct or coalesced at the posterior to form a 

 central bilobed plate; median septum long, slender, elevating pos- 

 teriorly and united to the inner hinge plates to form a small V-shaped 

 chamber which may be filled by callus in old specimens. Median 

 septum rising to a crest just anterior to the apex; cardinal process 

 a small, triangular, transversely striated pit at the apex; adductor 

 scars long and narrow, posteriorly situated. 



Type species. — Frieleia halli Dall, Proc. U. S. Nat. Mus., vol. 17, 

 p. 714, pi. 24, figs. 6, 9-13, 1895. 



Comparisons. — This is a thin-shelled, fragile brachiopod with both 

 valves somewhat sulcate in the Recent species and characterized by a 

 great development of inner hinge plates and a camerate apex in the 

 brachial valve. It is unlike all other described genera in these re- 

 spects. 



Geological horizon. — Possibly Miocene to Recent. Species from 

 the California Tertiary now referred to Hemithyris or other genera 

 may belong here. 



Assigned species: 



Frieleia halli Dall, Recent, West Coast North America, Japan. 



? Terebratula nitcns Conrad = Hemithyris astoriana Dall, Miocene, 



Oregon. 

 Hemithyris pellucida Yabe and Hatai, Recent, Japan. 



Distribution. — Known from Alaska to California, Japan, and Kam- 

 chatka in waters ranging from 21 to 1,059 fathoms. 



Discussion. — The important exterior features of this genus are 



