CONTRIBUTIONS TO PALEONTOLOGY. 189 



ATRYPA PSEUDOMARGINALIS(n.s.). 



Shell trilobate, subcircular, with the beak of the ventral valve extended. Dorsal 

 valve with mesial fold strongly defined below the first third of the shell, and 

 elevated in front. The mesial sinus does not extend to the beak. Plications 

 rounded, irregularly bifurcating. 



This species resembles j^trypa marginalis of Dalman, but is larger and more 

 robust, the beak less attenuate, the mesial fold and sinus broader and not extending 

 to the beak, and the striae coarser and not as much recurved. From the Bohemian 

 specimens under the same name, it differs in the greater elevation and rounded 

 form of the mesial lobe, and the less angular plications. 



Geological formation and locality. Upper Helderberg limestone : Schoharie. 



MERISTA HASKINI ( n.s.). 



Shell broadly ovate, more or less gibbous, length and breadth nearly equal, the 

 greatest width anterior to the middle. Dorsal valve often a little wider than long. 

 Ventral valve slightly the more convex, the greatest depth being a little anterior 

 to the umbones : beak extended and slightly incurved, and, in all the specimens 

 examined, truncated by a broad rounded foramen, impressed near the front by 

 a short shallow sinus which produces an arcuation of the dorsal valve in front. 

 Surface marked by close concentric lines of growth, which are crowded into 

 wrinkles on the sides of the shell. Interior substance of the shell fibrous, with 

 an exterior covering which appears to be punctate. 

 This shell bears many features of Terebratula. It differs from M. barrisi in 



the broader form, short and little defined sinus, and surface characters. 



Geological formation and locality. Shales of the Hamilton group, in Western 



New- York. 



MERISTA BARRISI (n.s.). 



Shell ovoid, more or less elongate or sometimes broadly ovate; proportions va- 

 riable. Ventral valve extremely arcuate : beak incurved; mesial depression 

 sometimes beginning about one-third the length below the beak, and becoming 

 on the front of the shell a broad flattened sinus produced in a short linguiform 

 extension. Dorsal valve little longer than wide, regularly convex, abruptly ele- 

 vated near the anterior margin from the extension of the mesial sinus of the 

 opposite valve. Surface smooth, or marked by regular concentric lines of growth; 

 some at the margins crowded into wrinkles. The exfoliated shells show obscure 

 radiating strige. 



This species presents considerable variety of form; due, in the specimens exa- 

 mined, both to stages of growth and to accidents of compression, and also to the 

 degree of development of the mesial sinus. 



Geological formation and locality. In limestone of the Marcellus shale, near 

 Leroy, N.York. From Rev. W. H. Barkis. 



MERISTA DORIS (n.s.). 



Shell subovate, elongate, compressed below the middle and the margins thin and 

 sharp, gibbous on the umbones. Ventral valve with the beak elongate, attenuate 

 and incurved; the sides below the beak abruptly compressed, making a concave 

 area; regularly convex from the beak to below the middle of the valve, where it 



