No. 109.] • 103 



above it, forming a low scniioval or semielliptical arch from 

 beak to front, sloping very gradually to tlie side?, wiiich (in old 

 specimens) are often so abruptly deflected, or even inflected, as 

 to form a distinct angular ridse extending from near the beak 

 two-thirds of tlie way to the front ; beak obtuse, scarcely in- 

 curved. Surface marked by regular simple radiating striae, some- 

 times crossed near the borders by distinct concentric wrinkles. 



This species varies greatly in form ; some individuals being very gibbous 

 and distinctly ovate, while others arc more or less compressed and very 

 elongate-ovate or narrow elliptical : the first variety was Eaton's T. 

 ovoides, and the latter his T. perovalis. After studying a large collection 

 of these forms, I am satisfied that they arc varieties of the same species, 

 rather than distinct types. 



I have some fine specimens from Cumberland ( Md.), apparently identi- 

 cal with this one ; but they are usually smaller than those found in New- 

 York, and appear to be a little more finely striated. 



Geological position arid locality. Oriskany sandstone, Helderberg and 

 Schoharie. 



Mkqaktbris ovoidei. 



