468 MISSISSIPPIAN BRACHIOPODA 



lar, the width three or four times the height, nearly filled with the 

 cardinal processes and the hinge-plate of the opposite valve when the 

 two valves are in articulation, the apex connecting with the foramen 

 which encroaches upon the beak; lateral slopes convex, the convexity 

 continuing to the cardinal extremities except rarely when the valve is 

 slightly compressed in that direction; mesial sinus more or less obscure, 

 rather narrow and ill-defined laterally, occasionally essentially obsolete, 

 sometimes rather deep, usually developed to a moderate degree, originat- 

 ing at or near the beak as a mesial flattening of the valve and becoming 

 more depressed towards the front. 



Brachial valve a little more convex than the pedicle, the 'greatest 

 convexity near or posterior to the middle, the surface curving rather 

 abruptly to the cardinal margin and more gently to the antero-lateral 

 margins ; the beak incurved beneath that of the opposite valve ; mesial 

 fold obscure, as usually developed it is a mesial flattening of the valve 

 slightly or not at all elevated posteriorly, and but little elevated an- 

 teriorly. 



Surface of each valve marked by more or less irregular, sub-parallel, 

 concentric, lamelliform extensions from one to three millimeters apart, 

 those towards the front of the shell becoming more crowded. Between 

 these stronger markings much fainter concentric markings may some- 

 times be detected. 



Remarks. This species is a close ally of A.^lamcllosa, and should perhaps 

 not be considered as distinct from it. There seems to be a constant 

 difference between the two species, however, in the smaller size of A. 

 hannibalensis and in its greater proportional length, its outline being much 

 more nearly subcircular. The concentric lamellae are also usually closer 

 together in this species, a feature which might be expected from its 

 smaller size. The character of the surface markings of the shell are 

 essentially the same in both forms. So far as it has been recognized, 

 this species is restricted in its distribution to the Kinderhook faunas. 



Horizon. Kinderhook. 



ATHYRIS PAPILIONIFORMIS McChesney 



Plate LXXVIII, Figs. 6-9 

 1860. Athyris spiriferoides McChemey, Desc. New Spec. Pal. Foss., p. 46. 



(Not A. spiriferoides Eaton, 1831.) 

 1865. AtJtyris papilioniformis McChesney, 111. New Spec. Foss., pi. 6, 



figs. 4a-c. 

 1868. Athyris ? papilioniformis McChesney, Trans. Chicago Acad. Sci., 



vol. 1, p. 33, pi. 6, figs. 4a-c. 



Description. Shell of medium size, the valves moderately convex, 

 wider than long, the greatest width near the cardinal margin, the hinge- 

 line nearly equal to the greatest width of the shell, the cardinal extremi- 



