276 PAUBONTOLOHY OF NEW YORK. 



This species is distinguished by its size, the moniliform siphuncle, and the 

 distance between the septa. 



In its vertical distribution it is found in the upper beds of the Hamilton, and 

 cannot be specifically distinguished from a form in the lower strata of the 

 Chemung, noticed below as a variety. 



Formation and localities. From the Hamilton group, in various localities in 

 Central New York. 



Orthoceras Bebryx, var. Cayuga, n. var. 



PLATES XXXIX, FIG. 1 ; LXXXVI, FIGS. 3-5 ; XCI, FIGS. 1-5 ; XCII, FIGS. 1-5. 

 Oi-thoeeras Bebryx, Hall. Illustrations of Devonian Fossils : Cephalopoda. Explanation of plate 39. 1S76. 



Numerous individuals have been observed among collections from the base of 

 the Chemung group which appear to be specifically identical with this species 

 as occurring in the Hamilton. The only difference noticed is the comparatively 

 deeper air-chambers, which are about as three to four in the two forms, when 

 measurements are made at points on the tube having the same diameter in 

 the different specimens. From the specimens included in this variety several 

 additional features have been observed, not clearly shown in the individuals 

 from the Hamilton group. The transverse section is circular. Chamber of 

 habitation cylindrical, well developed, its full extent not being observed. Septa 

 smooth and thin. Siphuncle excentric, distant from the dorsal and ventral 

 margins in the ratio of 3 to 7, or twelve and twenty-eight mm., where the tube 

 has a diameter of forty mm. 



A small individual, referred to this variety, embracing the greater portion of 

 the chamber of habitation and nine of the adjacent air-chambers, has a length 

 of 124 mm., and shows a broad, gentle constriction anterior to the middle of 

 the grand chamber. A larger specimen, consisting of a portion of the chamber 

 of habitation and nineteen air-chambers, has a length of 240 mm., of which 

 75 mm. pertains to the chamber of habitation, which has a diameter of fifty- 

 five mm. Large fragments of the grand chamber have been observed, having 

 a diameter of seventy-five mm. 



