100 [AsSEMBLT 



than the opposite, gibbous, transverse, or as wide as long : 

 mesial fold usually not defined above the lower third of the 

 shell ; its place above this being indicated by the straightness 

 of the striae and sometimes by a little greater gibbosity : hinge 

 line short ; the cardinal extremities rounded. 

 Surface marked by fine^ regular lam^llose strise, the edges of 

 which are sometimes projected. 



The distiDguishing feature of this species, when compared with the 

 three species known in the Hamilton group, is the great inequality of 

 "the valves. The band-like or lamellose strise are not Unlike the A. vittata, 

 but the elongate ventral valve and angular sinus are very distinctive 

 features. Internal casts of the species are strongly marked by the 

 generic characters of Athyris. 



Geological formation and locality. In the Chemung group : Philips- 

 burgh, Alleghany county, and elsewhere. 



MERISTELLA ELISSA ( n. s.). 



Shell subo.void ; length and width of the body of the shell sub- 

 equal, with a linguiform extension in front. Ventral valve 

 gibbous and extremely arcuate, the umbo much elevated, and 

 the beak incurved over the dorsal valve : the greatest gibbosity 

 of the valve is a little below the beak of the dorsal valve ; 

 the base extended in front, with scarcely a sinus. Dorsal 

 valve depressed-convex below the middle, a little gibbous 

 above, broadly expanded laterally, and extended in front into 

 a broad linguiform process. 



Surface marked by fine concentric strise, with stronger lamellose 

 elevations at intervals, and obscure radiating strise crossing 

 these. 



The specimen described has a length of one inch and eight-tenths, 

 and, below the beak of the ventral valve, is about one inch and four- 

 tenths; while the greatest width across the middle of the shell is more 

 than one inch and five-tenths. The width of the linguiform process, in 

 the middle of its extension, is about seven-tenths of an inch. 



This species is distinguished from M. nasuta of Conrad by its larger 

 size, comparative flatness of dorsal valve, and broad extension in front ; 

 while in that species it is narrow, and more incurved and elevated in 

 front. 



Geological formation and locality. In the Schoharie grit : Helderberg 

 iduntatns. 



