17(1 PALEONTOLOGY OF NEW YORK. 



Beaks acute, prominent, directed forward, anterior t<> the middle <>f the 

 shell. Umhonal region gibbous, subtending an acute angle. 



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



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

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

 its height, defined by a change in the direction of the surface stria 3 ; margin 

 gently concave ; extremity acute. 



Test thin, marked by line concentric stria', and at regular intervals by 

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

 interior, a regular handed surface. These stronger stria 1 are closely arranged 

 on the anterior side and ear. while on the posterior side they preserve their 

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

 elevated concentric striae. En 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 lli mm., hinge-line about 

 LO mm. Another example has a length of 12 mm., height 13 mm., and 

 hinge-line about 11 mm. 



The 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 of the Hamilton group ; shores of 

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



Leiopteria Oweni. 



PLATE XX, FIG. 10. 



Leiopteriu Oweni, Hall. Pal. N. Y., vol. v. pt. 1 Plates and Explanations : PI. 20. 6g. in. Jan., L883. 



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

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

 Left valve coin ex, umbo gibbous, beak elevated. Bight valve concave 



