PLATE LXXXV. 



Obthoceras exilb. 



rage 290. 

 See Plates 39, 84. 



Fig. 1. The chamber of hahitation, with two of the attached aii'-chamber8, showing the regijlar enlarge- 

 ment of the tube to the aperture. 



Fig. 2. A septum of the jn-eceding, showing the circolaj-, transVei-se section of the tube and the excehtric 

 position of the eiphiincle. 



Fig. 14. A chamlwi'ed fragment of an individual i-eferred with doubt to this species. The specimen has 

 been much macerated and distorted in the soft shales, which has obscured the specific chai-ao- 

 ters. The exterior shows numerous furrows where the shell has been invaded by some 

 tei-ebrous animal. East shore of Cayuga lake, N. Y. 



Fig. 15. A specimen in the same association, and similar to the preceding. The apparent expansion and 

 constriction of the tube is due to the action of iron pyrites. 



ORTnocERAs Telauon. 



P«Ke 291. 

 Fig 8. Tlie chamber of habitation of an example, showing its cylindi-ica! form and the absence of any con- 



strirtion or expniision at the apertui-e. 

 Fig. 4. A septum of the preceding, showing the transverse section of the tube and the very excentric 



position of the siphuncle. 

 Fig. 12. Ventral view of a small, rhambei-ed fragment, showing the depth of the chambers and the gradual 

 enlargement of the tube. A low, longitudinal carina along the ventral side is not rejjresented. 

 The specimens of this species here reprepented aie from the shales of the Hamilton group, at 

 Monteith'g Point, Canandaigtta lake, N. Y. 



Orthoceras constrictcm. 



P.ige 288. 



See Plate 84. 



Fig. 5. A fragment of the chiiraber of habitation, with two of the attached air-chambers, showing a decided 



constriction of the tube at the upper extremity. Cazenovia, N. Y. 

 Fig. 10. A fragment re'aining a portion of the chamber of habitation and twenty-one air-charabere, showing 



the very gradual inci-ease in their depth toward the grand chamber. Cazewmia, N. Y. 

 Fig. 11. A chambered fragment, retaining neai'Iy its nomial form and pi"oportions. Monteith'8 Point, 



Canaiidaigua lake, iV". Y. 

 Fig. 13. A .septum of another fragment, showing the position of the siphuncle and the circular, transveree 



section of the tube. Monteith's Point, Canandaigim lake, N. Y. 



Orthoceras spissum. 



Piige 287. 



Rg. 6. A fragment embracing a portion of the chamber of habitation and fifteen air-chambers, showing the 

 frequency of the septa and the regulai- depth of the air-chambere. Pratt's Falls, Onoiidaga 

 county, N. Y. 



Fig. 7. A septum of the pi-eceding, showing the position and size of the siphuncle. The section as repre- 

 sented is nearly circular, whereas the transverse section of the tube is broadly elliptical. 



Fig. 8. A portion of a larger individual, exhibiting the same charactera as the preceding example. Pratt's 

 Falls, Onondaga county, N. Y. 



Fig. 9. A septum of the jireceding specimen, showing the position of the siphuncle. This figure is also too 

 nearly circular in outline. It should be flattened in a dorso-ventral direction. 



