NO. 5 RHYNCHONELLOID BRACHIOPODS — COOPER 33 



Eocene species is not so strong in the specimens examined. This 

 however could hardly be regarded as a generic difference. Other 

 species of Eohemithyris can be expected in other Tertiary deposits 

 and should be looked for. 



Rhynchonella grayi Woodward is another species that has never 

 been correctly placed generically. Through the kindness of Dr. Helen 

 M. Muir-Wood and the authorities of the British Museum I am able 

 to furnish exterior and interior views of this species. It is clearly 

 very similar to Hemithyris columns but is more strongly costate in 

 the anterior third. Eohemithyris alexi and columns are both ob- 

 scurely to definitely costate in the anterior part. Davidson's figures 

 of R. grayi greatly exaggerate the plication. The interiors and beak 

 characters of R. grayi are clearly identical to those of E. columns 

 and E. alexi, except for the swellings of shell material on the hinge 

 plate, consequently the species is assigned to Eohemithyris. The shell 

 profile and beak characters exclude R. grayi from assignment either 

 to Basiliola or Rhytirhynchia. Lack of inner hinge plates separates 

 R. grayi from Aetheia which, except for the anterior costation, it 

 otherwise resembles in its exterior characters. 



EOHEMITHYRIS? GETTYSBURGENSIS Cooper, new species 

 Plate 8, B 



Shell large, subpentagonal in outline, slightly wider than long; 

 sides narrowly rounded ; widest slightly anterior to midvalve ; anterior 

 commissure strongly uniplicate; surface marked only by concentric 

 lines of growth. 



Pedicle valve less deep than the brachial valve, moderately convex 

 in lateral profile and with the strongest convexity in the posterior 

 third ; anterior profile nearly flat but with the median region slightly 

 concave ; beak low, incurved ; umbo moderately swollen ; sulcus origi- 

 nating on the umbo, shallow and narrow but deepening and widening 

 anteriorly to occupy slightly more than half the width at the anterior ; 

 flanks somewhat flattened and with gentle slopes to the margins ; 

 tongue moderately geniculate, moderately long and broadly rounded. 



Brachial valve gently and fairly evenly convex in lateral profile; 

 anterior profile moderately strongly domed ; fold originating at about 

 midvalve, low, flattened, and prominent only at the anterior; flanks 

 bounding fold slightly depressed, gently rounded. Umbonal region 

 only slightly convex. 



Interior. — Strong, short dental plates visible in pedicle valve; 

 small, short socket ridges visible in brachial valve but no trace of a 

 median septum or ridge seen through the moistened shell. 



