NO. 5 RHYNCHONELLOID BRACHIOPODS — COOPER 41 



Aphelesiinae Cooper, new subfamily 



APHELESIA Cooper, new genus 



(Gr. apheles, smooth) 



Plates 7, B, 8, C, 22, D 



Outline subtriangular to subpentagonal ; widest anterior to the 

 middle ; strongly inequivalve, the brachial valve being deep and swol- 

 len, the pedicle valve gently convex ; anterior commissure strongly 

 uniplicate but fold of brachial valve defined only at the anterior; 

 smooth on most of the surface but the anterior with incipient costa- 

 tion. Beak of pedicle valve moderately elongated, nearly straight to 

 suberect, pointed ; foramen complete, elongate-oval, small hypothyrid ; 

 deltidial plates thick, conjunct, moderately auriculate; beak apex 

 thickened internally. 



Pedicle valve interior with elongated, corrugated teeth supported 

 by thick dental plates. Muscular field large and flabellate, extending 

 to about midvalve with the diductor scars surrounding the adductors ; 

 adjustor scars small and laterally disposed. 



Brachial valve interior with deep corrugated sockets bounded by 

 strong overhanging socket ridges ; crura of falcifer type, long, cres- 

 centic in section, broad, scimitarlike and cemented directly to the 

 socket ridges with no outer hinge plates developed ; inner hinge plates 

 lacking ; crural supporting plates thick. Median ridge low and thick ; 

 adductor field narrow and elongated. Pallial trunks not deeply im- 

 pressed. 



Type species. — Anomia bipartita Brocchi, Conch. Foss. Subapp., 

 vol. 2, p. 469, pi. 10, fig. 7, 1814. 



Comparisons. — This species is generally referred to Hemithyris 

 but it actually does not have either the exterior or interior features 

 of this genus. Aphelesia is completely smooth or with slight and very 

 obscure costation. It does not have the numerous and regular sub- 

 dued costellae or striae of Hemithyris. Furthermore the foramen of 

 Aphelesia is small and the deltidial plates are conjunct. The foramen 

 of Hemithyris is large and not enclosed anteriorly because the deltidial 

 plates are disjunct. 



The interior of the pedicle valve of each of these genera is quite 

 similar except for the fact that the dental plates of Hemithyris are 

 somewhat more prominently developed and with deeper umbonal 

 chambers than those of Aphelesia. Important differences appear on 

 the inside of the brachial valves where the cardinalia of the two 

 genera are quite distinctive. In Hemithyris the crura are of radulifer 



