446 MISSISSIPPIAN BRACHIOPODA 



1895. Eumetria vera var. co'stata Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 

 pi. 51, figs. 27-33. 



Description. Shell attaining a medium size, longer than wide, the hinge- 

 line very short, the greatest width anterior to the middle, subovate in 

 outline, the lateral margins diverging from the beaks nearly to the line 

 of greatest width in straight or slightly convex lines, anteriorly the 

 outline is subsemicircular, sometimes with a slight straightening of the 

 margin in the center. The dimensions of two individuals are: length 

 of pedicle valve 30 mm. and 27 mm., length of brachial valve 26 mm. and 

 23.5 mm., greatest width 28 mm. and 23 mm., thickness 16 mm. and 15 

 mm., length of hinge-line 6 mm. and 7 mm. 



Pedicle valve most convex posterior to the middle, the umbonal region 

 projecting notably beyond the hinge-line; the curvature of the surface 

 from the beak to the anterior margin has a regularly decreasing convexity, 

 the convexity to the lateral margins becoming gradually more abrupt 

 anteriorly; towards the cardinal extremities the surface is inflected, and 

 at the cardinal extremities the surface is again deflected to form a pair 

 of minute, sometimes almost obsolete, auriculations ; the beak is prom- 

 inent and incurved, and is pierced by the large, subcircular foramen, 

 which encroaches notably upon the umbonal region; the cardinal area 

 small, arched, its lateral margins sharply defined, sloping regularly from 

 the sides of the beak to the cardinal extremities, the delthyrium closed 

 by the pseudo-deltidium, only its apex being in contact with the foramen ; 

 mesial portion of the valve not depressed in a sinus, but sometimes the 

 surface of the valve is flattened along an undefined mesial band, especially 

 towards the front. 



Brachial valve a little less convex than the pedicle, the greatest con- 

 vexity posterior to the middle, the beak projecting slightly beyond the 

 hinge-line, the surface curving somewhat abruptly from the umbonal 

 region towards the cardinal extremities, but again deflected just before 

 it reaches these extremities to form a pair of small auriculations a little 

 more conspicuous than those of the pedicle valve; anteriorly from the 

 beak to the front of the valve the surface describes a gradually decreasing 

 convex curve and laterally the curvature becomes gradually more convex 

 in passing from the anterior margin towards the hinge extremities. 



Each valve is marked by from 30 to 40 regular, simple, depressed, 

 rounded, nearly uniform, radiating plications, which increase regularly 

 in size in passing from the beak to the front. Growth lines are either 

 lacking or are inconspicuous. The shell structure is minutely punctate. 



Remarks. This shell was originally described as a variety of E. vera, 

 and has sometimes been considered along with that species, as synonymous 

 with E. verneuilana. It is not improbable that all of these forms 

 might be shown to be united by intergradations, yet it seems advisable 



