PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 663 
OLIGORHYNCHIA sp. 1 
Plate 268, I, figures 41-44 
A few specimens of Oligorhynchia were taken from a limestone 0.7 mile south 
of Mooney Cemetery on the Bulls Gap (T.V.A. 171-SE) Quadrangle. The hori- 
zon represented is either high in the Benbolt or low in the Wardell formations 
(=Dryden formation where indivisible). It is uncertain which is the correct 
horizon, but the specimens occur a considerable distance above a sandstone 
containing Dinorthis transversa Willard. 
The specimens appear not to belong to O. bifurcata because they do not possess 
the characteristic forking of the median fold in the brachial valve. The specimens 
are like O. angulata, but the fold of the brachial valve seems to be lower and the 
shell is not so wide anteriorly. 
Figured specimen.—118018a. 
SPHENOTRETA Cooper, new genus 
(Greek sphen, wedge; tretos, opening) 
Shell small, triangular to oval in outline, apical angle acute; anterior commis- 
sure more or less deeply sulcate; surface costate. Foramen large, longitudinally 
elliptical or oval; deltidial plates small, triangular, located at the anterior end 
of the foramen. 
Pedicle interior with short divergent dental plates. Other details not determin- 
able in material available. 
Brachial valve with divided hinge plate; crural bases small, triangular ; crura 
long and slender, directed obliquely anteriorly and slightly toward the pedicle 
valve. 
Genotype.—S phenotreta cuneata Cooper, new species. 
Discussion.—All the material on which this genus is based consists of small 
specimens, mostly below 5 mm. in length. Generally the shells are filled with 
crystalline calcite, but the structures are so delicate that they are only visible 
with difficulty when the shell is removed. The members of this genus have 
hitherto been placed under Zygospira, this association having been inspired by 
the strong pedicle folding and deep sulcation of the brachial valve which are 
features of the early spire-bearer. All details of the interior of Sphenotreta de- 
termined in this work indicate that this genus is a rhynchonellid and not an early 
spire-bearer. Of the many specimens dissected not one showed any trace of a 
spire. 
This genus is similar to OligorhyncMia in external form and interior. The type 
of folding is similar in the genera except that Sphenotreta does not develop a 
fold in the brachial sulcus. The two genera differ in ornamentation rather 
strongly. Oligorhynchia has a few strong costae only, whereas Sphenotreta is 
wholly costate. 
Internally the two genera are similar in having long, slender crura. Further 
comparison is almost futile because details of the hinge plate of Sphenotreta are 
not yet determined. It is evident, however, from what can be seen, that Spheno- 
