424 MISSISSIPPIAN BRACHIOPODA 



to the cardinal margin and a little more gently to the lateral and an- 

 terior margins; beak obtuse, scarcely incurved; cardinal area high, the 

 inferior portion nearly flat, and lying at an angle of about 90 degrees to 

 the plane of the valve, becoming a little arched towards the beak, the lat- 

 eral margins not defined, the surface curving with almost no demarcation 

 into the lateral slopes of the valve; the delthyrium large, open, a little 

 higher than wide ; the lateral slopes convex, smooth ; mesial sinus narrow 

 and shallow, rounded in the bottom, not sharply defined laterally, orig- 

 inating in the umbonal region anterior to the beak, sometimes nearly or 

 quite obsolete. 



Brachial valve nearly flat, the beak obtusely pointed and produced 

 horizontally a little beyond the hinge-line, the surface most prominent 

 in the umbonal region, a little compressed towards the cardinal ex- 

 tremities, the mesial portion of the valve depressed in a broad, shallow, 

 ill-defined sinus which originates at about the posterior third of the 

 valve and widens rapidly until it occupies nearly one-half the total 

 width of the valve towards the front. 



Both valves are entirely non-plicate, but the surface is completely 

 covered with minute, imbricating spines in perfectly preserved specimens. 



Remarks, This species occurs in great numbers in the shaly partings 

 near the base of the Louisiana limestone, many complete examples being 

 recovered from the washings. The species is characterized by its minute 

 size, by the gibbosity of the pedicle valve and its obtuse beak, and by 

 the character of the minute surface markings. 



Horizon. Louisiana limestone of the Kinderhook. 



AMBOCCELIA PARVA Weller 

 Plate LXXVII, Figs. 32-35 



1899. Ambocoelia parva Weller, Trans. St. Louis Acad. Sci., vol. 9, p. 20, 

 pi. 4, figs. 1-4. 



Description. Shell small, subovate in outline, the length and width 

 equal or the width greater than the length, the hinge-line shorter than 

 the greatest width of the shell, the cardinal extremities rounded. The 

 dimensions of two pedicle valves are : length 4.7 mm. and 3.4 mm., width 

 4.8 mm. and 3.6 mm., convexity 2.3 mm. and 1.3 mm. 



Pedicle valve strongly convex, the greatest convexity posterior to the 

 middle, the umbonal region projecting notably beyond the hinge-line 

 posteriorly; the surface somewhat flattened in the median region from 

 the beak to the anterior margin, laterally the surface curves abruptly 

 towards the cardinal extremities and a little more gently to the lateral 

 margins; beak obtusely rounded, moderately incurved; cardinal area of 

 moderate height, arched, apparently not sharply defined at its lateral 

 margins, the surface curving into the lateral slopes of the valve without 



