CEPHALOPODA. 27 



The only related species from the Upper Helderberg group, which also ap- 

 parently has a slight normal curvature in the tube, is 0. Ohiocnse (Pal. N. Y., 

 vol v, pt. 2, p. 236), from which the present form may be distinguished by its 

 larger size and deeper air-chambers. 



The specimen is a weathered and macerated internal mould, and many of 

 the important specific features of test, ornaments and septa have not been 

 preserved. 



Distribution. In the Upper Helderberg limestone, at Cherry Valley, Otsego 

 county. 



Orthoceras directum. 



PLATE CXV1I, FIGS. «, 7. 

 OrOwceras directum. Hall. Fifth Aim. Rept. State Geologist. Expl. pi. (117) 1. figs. 6, 7. IS86. 



Shell large, straight, gradually increasing in diameter to near the aperture. 

 Apical angle seven degrees. Initial extremity unknown. 



Chamber of habitation large ; length one and a half times the diameter of 

 the tube at the last septum. Air-chambers varying from 8 to 12 mm. in 

 depth in the distance of 100 mm. near the outer chamber. 



Septa thin, moderately concave. Sutures direct. 



Siphuncle and test not preserved in the specimen described. 



Internal mould smooth. 



The specimen consists of the chamber of habitation and twelve attached 

 air-chambers, and has a length of about 250 mm., of which 115 mm. pertain 

 to the chamber of habitation. 



Figures 6 and 7 of plate cxvii, show in a very marked degree a condition 

 frequently present in fossils of this class. Figure 6 shows the internal mould 

 with the air-chambers well defined and the sutures depressed from the weather- 

 ing of the septa, presenting every evidence of the preservation of the septa 

 and siphuncle. A section of the specimen, represented in figure 7, shows that 

 nearly the entire interior of the shell has been broken away, and that Tenta- 

 culites and other shells were drifted in with the sediments filling the tube. 



Distribution. In the Corniferous limestone, Delaware, Delaware county, Ohio. 



