17(1 PAL.EOMVLOGY OF MCW YORK. 



Beaks acute, prominent, iliii-oteil t'orwanl, anterior to tlie middle of the 

 shell. Umbonal region gibbous, subtending an acute angle. 



Ear small, straight on the upper margin ; marked by an oblique fold, and 

 separated Worn, the body by an abrupt sulcus and a well-defined byssal sinus. 

 Wing small, triangular, joining the body of the shell below the middle of 

 its height, defined by a change in the direction of the surface strije; margin 

 gently concave ; extremity acute. 



Test thin, marked by line concentric striai, ami at reiiulai' intervals In- 

 stronger elevated stria?, which give to the macerated shell, and the cast of the 

 interior, a regular banded surface. These stronger strise are closely arranged 

 on the anterior side and ear. while on the posterior side they ])reserve their 

 equidistant character. The right valve is very distinctly marked by the 

 elevated concentric stria\ In both valves there are radiating lines which 

 apparently belong to the structure of the shell. 



Interior unknown. Ligamental area narrow. 



One specimen has a length of 13 mm., height 111 nini., hiiiLie-line aiiout 

 in iiiui. Another example has a length of 12 iiiui., height \o mm., and 

 hinge-line about 1 I mm. 



Tiie small size, erect ovate form, short hinge-line, the proportions of height 

 and length, and the surface characters, distinguish this species from every other 

 form here described. 



Formation and localities. In the soft shales t)l' the Hamilton group ; shores of 

 Canandaigua lake, and at Norton's Landing, Cayuga lake, N. Y. 



Leiopteria Oweni. 



PLATE XX, FIG. 10. 

 Leiopter'm Oweni, Halt,. Pal. N. V., vol. v, |it. 1 Pliitos ami Explauatioii.s : PI. 20. tifr. 10. .Ian.. 1883. 



Shell quite large, sub-rhomboidal ; body broadly ovate, oblique to the hinge- 

 line; length greater than the height; margins rounded, produced posteriorly. 

 Left valve convex, umbo gibbous, beak elevated. Right valve concave 



