l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



foramen, concave deltidial plates, reduced to obsolete dental plates 

 and thick inner hinge plates. 



Genera : Aetheia and Patagorhynchia. 



Acthcia. — Elongate triangular in outline and exterior smooth. 

 Patagorhynchia. — Costellate and anteriorly imbricate. 



Family Hemithyridae Rzhonsnitzkaia, 1956 [proposed as a sub- 

 family]. — Rhynchonelloidea with strong, slender, curved radulifer 

 crura attached to small outer hinge plates by their posterodorsal face 

 or to thick socket ridges; crura distally pointed and horizontally 

 flattened. 



Genera: Hemithyris, Notosaria, Tegulorhynchia, and Plicirhyn- 

 chia. 



Hemithyris. — Beak long, surface striate to costellate; deltidial plates disjunct. 



Notosaria. — Beak short ; exterior costate ; nonimbricate ; deltidial plates dis- 

 junct. 



Tegulorhynchia. — Costellate to costate, strongly imbricate to spinose ; deltidial 

 plates conjunct?; medium septum reaching apex. 



Plicirhynchia. — Long beak, posterior striate to costellate, anterior costate to 

 plicate; deltidial plates conjunct. 



Frieleiidae Cooper, new family. — Usually capillate to costellate 

 valves with triangular outline, strong dental plates, and brachial valve 

 with short, straight, laterally compressed spinulifer crura supported 

 by short plates that unite with the median ridge or septum to form a 

 small chamber. 



Genera: Frieleia, Compsothyris, Grammetaria. 



Frieleia. — Elongate shells with the pedicle valve having the greater depth 

 and the brachial valve with a high median septum; anterior commissure recti- 

 marginate to ligate; deltidial plates disjunct; inner hinge plates extravagantly 

 developed. 



Compsothyris. — Roundly triangular in outline ; valves of subequal depth ; 

 median septum only moderately elevated and deltidial plates disjunct; anterior 

 commissure gently uniplicate; inner hinge plates incipiently developed. 



Grammetaria. — Elongate, costellate shells with rectimarginate anterior com- 

 missure, low, thick median septum, and conjunct, strongly auriculate deltidial 

 plates; inner hinge plates incipient. 



Hispanirhynchiidae Cooper, new family. — Triangular, capillate 

 rhynchonelloidea having a weak median ridge or no median ridge in 

 the brachial valve; crura spinulifer; anterior commissure rectimargi- 

 nate to ligate. 



Genera: Hispanirhynchia and Sphenarina. 



Hispanirhynchia. — Deltidial plates disjunct and median ridge of brachial valve 

 low and thick; inequivalve, the pedicle valve being the deeper; inner hinge 

 plates strongly developed. 



