CONTRIBUTIONS TO PAL.EONTOLOGT. 75 



an inch. A still larger fragment has a diameter of seven-eighths of 

 an inch. 



This species is readily distinguished from any other known to me in the 

 whole series, by its slender and almost cylindrical form. 



Geological forviation and locality. In the Schoharie grit at Schoharie. 



ORTHOCERAS THOAS ( n. s.). '/ ['■'j • ^/ - 

 Shell cylindrical, very gradually tapering towards the apex : outer 

 chamber deep; septa very concave, the concavity exceeding the 

 distance between them. Siphuncle small, central. 

 Surface annulated by strong direct ridges just above ( or on the 

 apicial side) of each septum ; longitudinally striated by coarse 

 rounded strise, which are distant from each other nearly twice 

 their width : these striae are usually rigid, but sometimes undu- 

 lated. 



Nearly all the specimens are a little flattened from compression, 

 the greatest diameter being in the direction of the laminae of the 

 rock. A specimen one inch in diameter between the annulations 

 measures about one-eighth of an inch more across the annulations. 

 The distance of the annulations is not always uniform : in two 

 specimens of nearly the same size, one has nine annulations in the 

 space where the other has eight. In a specimen of an inch in dia- 

 meter, the siphuncle measures a little over three-twentieths of an 

 inch. 



The ridges or annulations are direct, and, in this character, differs from 

 the Niagara species, while the longitudinal striae constitute another distinc- 

 tive feature. This fossil is less tapering than the annulated species in the 

 Hamilton group. 



Geological formation and locality. In the Schoharie grit : at Schoharie 

 and the Helderberg mountains. 



ORTHOCERAS HYAS ( n. 8.). y' A "' 

 A fragment in the same association as the preceding has a slight- 

 ly smaller central siphuncle and less concave and more closely 

 arranged septa, there being four in the space occupied by three in 

 the former. The annulations are a little more abruptly elevated than 

 in 0. thoasj and are direct across the middle of the chamber, or 

 equidistant between the septa. 

 1861.1 



