46 , SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



Hemithyris d'Orbigny, Bronn, Neues Jahrb. Min., Geog., Geol. u. Petrefaktenk, 

 p. 246, 1848; Thomson, Geol. Mag., dec. 6, vol. 2, p. 387, 1915; Thomson, New 

 Zealand Board Sci. Art, Manual 7, p. 149, 1927; Grabau, Sci. Quart. Nat. 

 Univ. Peking, vol. 3, No. 2, p. 112, 1932; Hatai, Sci. Rep. Tohoku Imp. 

 Univ., ser. 2 (Geology), vol. 20, p. 194, 1940. 



Outline triangular, greatest width at or anterior to the middle; 

 inequivalve, the brachial valve having the greater depth and con- 

 vexity; anterior commissure broadly to narrowly uniplicate; surface 

 obscurely to moderately costellate, the costellae broad and separated 

 by fine striae. Beak of pedicle valve prominent, elongate, and sub- 

 erect. Foramen incompletely hypothyrid ; deltidial plates disjunct ; 

 apical region thickened and buttressed by a short median ridge. 



Pedicle interior with strong, somewhat elongated, corrugated teeth ; 

 dental plates vertical and strong, the umbonal cavities becoming par- 

 tially filled by adventitious deposit in old specimens. Delthyrial 

 cavity occupied by the pedicle. Apical plate thick, commonly some- 

 what elevated. Muscle field anterior to the delthyrial cavity, sub- 

 flabellate, the diductor scars surrounding the adductors. Adjuster 

 scars lateral to the diductors. Lateral areas bounding muscle field 

 pitted ; pallial marks obscure. 



Brachial valve with deep, corrugated sockets defined by strong 

 crural supporting plates ; socket ridges prominent ; crura of radulif er 

 type, long, slender, curved, forming horizontally flat blades distally, 

 widening posteriorly to form a narrow hinge plate and strengthened 

 anteriorly by an oblique ridge running from the outside of the tip to 

 the inside of the hinge plate ; crural supporting plates buttressing 

 hinge plate; inner hinge plate absent or incipient. Cardinal process 

 absent, the diductor muscles being attached to an apical, roughened 

 pit. Median ridge low, defined chiefly at midvalve and disappearing 

 posteriorly in the umbonal chamber. Adductor field small consisting 

 of a large pair of triangular anterior scars and a pair of small, 

 elongate, subrhomboidal scars situated on the outside posterior to 

 the anterior set. 



Type species (by subsequent designation, d'Orbigny, 1847). — 

 Anomia psittacea Gmelin, Syst. Nat., vol. 2, p. 3348, 1790. 



Comparisons. — The exterior and interior details of Hemithyris are 

 distinctive and have no known close counterparts among the Tertiary 

 and Recent brachiopods. The genera nearest like Hemithyris are 

 Aphelesia and Notosaria. The former differs from Hemithyris in 

 being exteriorly smooth and in having broad, concave, falcifer crura. 

 The external form of Notosaria is suggestive and the beak charac- 



