278 TWENTIETH REPORT ON THE STATE CABINET. 



ElCHWALDIA CORALIFERA (Hall). 



Atrypa coralifera, Hall : Palaeontology of New-York, page 281, 1852. 

 This species occurs in the Niagara Shale at Lockport and Rochester. 



ElCHWALDIA RETICULATA (Hall). 



Rhy nchonzlla ? reticulata^ Hall : Transactions of the Albany Institute, 

 Vol. iv, page 217, 1862. From the Niagara group at Waldron, Indiana. 



ElCHWALDIA GIBBOSA ( n.S.). 



Shell ventricose, rather above the medium size, subtriangular or broadly 

 ovate in outline ; baso-lateral angles abruptly rounded, and the anterior 

 border straight or scarcely emarginate. Ventral valve strongly convex in 

 the umbonal region, becoming very slightly depressed on the anterior 

 part by a broad undefined sinus, which extends one half the width of 

 the shell : beak small, pointed and strongly incurved over that of the 

 opposite valve ; the denuded surface of the beak small. Dorsal valve a 

 little more gibbous than the ventral, very prominent in the upper half; 

 the anterior part occupied by a broad undefined elevation which is barely 

 distinguishable from the general convexity of the valve. Surface reticu- 

 lations very fine, about three or four in the space occupied by one on 

 the E. coralifera, and two or three to that of one on E. reticulata. 



This species may be distinguished from either of the other species of the 

 genus, by its greater gibbosity, even surface, and by the much finer reticu- 

 lations of the exterior structure. 



Geological formation and locality. — In rocks of the age of the Niagara 

 Group, in Perry and Decatur counties, Tennessee. 



ElCHWALDIA CONCINNA (n.S.). 



Shell small, sub-triangular in outline, a little wider than long, broadly 

 rounded in front, nearly straight in the middle, and more abruptly 

 rounded on the baso-lateral angles. Valves somewhat regularly convex ; 

 the ventral valve a little more elevated than the opposite, and having a 

 broad undefined sinus on the anterior half of the shell : umbo prominent ; 

 beak small and closely incurved, the nude space longer than wide. Dorsal 

 valve regularly convex, without visible trace of mesial elevation. Surface 

 reticulation fine ; pits elongate in the direction of the length of the 

 shell ; interspaces a little flattened on the surface. 



This species diifers from E. coralifera of New- York, in its general broad 

 triangular form, absence of mesial elevation on the dorsal valve, and unde- 

 fined sinus on the lower part of the ventral valve ; in the finer reticula- 

 tions, as well as the flattening of the interspaces. From E. reticulata it 

 diff"ers in the finer and more elongate pits and entire absence of mesial 

 fold : although that species sometimes has a scarcely defined fold, yet the 

 reticulation is always much coarser. 



Geological formation and locality. — In rocks of the age of the Niagara 

 or Lower Helderberg, Tennessee. 



