302 PALEONTOLOGY OF NEW YORK. 



Oethoceras Thestor, n. sp. 



PLATE LXXXII, FIG. 18. 



Shell straight, regularly and gradually enlarging. Transverse section circular. 

 The characters of the chamber of habitation, air-chambers, septa and 

 siphuncle are unknown. 



Tube ornamented with very numerous, sharp annulations. The annula- 

 tions are straight and horizontal, and about twelve in the space of ten mm. 

 Surface marked by regular, fine, longitudinal striae, crossed in the furrows 

 between the annulations by sharp, transverse striae. The longitudinal striae, 

 of which there are ten in the space of two mm., are continuous over the 

 annulations, crenulating their summits. 



This species is distinguished by the extreme frequency and regularity of the 

 annulations, in which it differs from the other annulated forms. The surface 

 characters are also different from those in O. lima. In 0. Idmon the annulations 

 are more abruptly elevated and less frequent ; being as seven to twelve in the 

 two species, with the intermediate furrows flattened. 



Formation and locality. From the carbonaceous beds of the Marcellus shales 

 of the Hamilton group at Schoharie, N. Y. 



Ortiiocekas Idmon, n. sp. 



PLATE XLI1I, FIGS. 11, 12. 



Shell straight, regularly enlarging. Transverse section, chamber of habitation, 

 septa and siphuncle not observed. 



The air-chambers are regular, as frequent as the annulations, or having a 

 depth of 1.5 mm. Sutures straight and horizontal. 



Test thin. Tube ornamented by numerous, regular, abruptly elevated 

 annulations, with flattened interspaces; of which there are seven in the 

 space of ten mm. Surfiice marked by regular, fine, continuous, longitudinal 

 striae, with concentric lines of growth in the furrows. 



The specimen figured has a length of forty mm., and preserves twenty- 

 five annulations in this space. 



