36 Bulletin 6 36 



the charaAer of the median fold, whether single or duplicate, and 

 the presence or absence of a plication in the sinus. In fihy 

 specimens examined, from 200 to 385 feet above the upper Port- 

 age ►S. l^vis zone, the number of plications varied from 12 to 24, 

 the average number being 16. A very small per cent., perhaps 

 one in 50 or 60, of specimens from the horizon of Triphammer 

 falls and Eddy's dam (385 feet above the >S. /(zvis zone) show a 

 duplicate median fold, and about the same number show a trace 

 of a plication in the sinus. Neither of these characfters have 

 been noticed in specimens from below this horizon. All of the 

 specimens which were properly preserved, show the distincft me- 

 dian septum extending nearly through the muscular scars in the 

 ventral valve. The greatest amount of variation, however, is 

 in the extent of the hinge line. In some specimens, the hinge 

 line does not extend beyond the margin of the valves, while in 

 others its delicate spine-like projedlions more than equal the width 

 of the valves. 



Spirifer Icevis Hall. 



Prof. Williams has reported this species from the upper part 

 of the Ithaca group and the writer has found several specimens 

 of it 130 feet below the upper Portage 6". Icsvis zone, so that this 

 species is now known to have a vertical range of not less than 

 500 feet. 



Spirifer fimbriata Morton. 



IvOwer part of the Ithaca group. — H. S. Williams. 



Spirifer angusta Hall. 



Lower Ithaca group. — H. S. Williams. 



Spirifer mesastrialis Hall. 



This is a very abundant species in the Ithaca group. It has 

 not been found in the Portage. 



Orthis impressa Hall. 



This is one of the charadteristic fossils of the Ithaca group. 

 Most specimens have the length and breadth nearly equal, both 

 dimensions averaging i y>^ inches. The Chemung form of this 

 species differs from that at Ithaca, according to Prof. Williams, 

 by having the shell wider than long. 



Rhynchonella {Stenoschisma) exiinia Hall. 



Occurs through the greater part of the Ithaca group. 



