I'LATK CXII. 



Orthoceras rudicula. 



Page »«. 

 See Plate 37. 



Fiir- 1. A lonfHtiidinHl nection of the lower portion of the si>ec,imen figtired on plate 37, showing the traces of 

 an expnndeil siphiincle, and the organic deposit on the concave piiles of the septa, rcprepeiited 

 in the tigure by a darker shade. Whei-evei' there is a separation of the air-chambera at the 

 septa, the origin of the raiseil ai-eola ai-ound the insertion of the sii^huncle is seen to be liue to 

 the organii; deposit on the peripheral portions of the septa. 



Fi|f. 2. A septum of the preceding indiviilnal, showing the raised areola, with a furrowed margin, produce<l 

 by the organic depo.«it on the concave side of the sejjtuni. The dei)08it is continned over 

 nearly the whole surface of the se)itnni, and presents little variation in its appearance. Upper 

 Hflderberg limestone. Stafford, AT. i'. 



Orthoceras sikpds. 



Page 269. 



Fig. E. An individual preserving the chamber of habitation and four air-chambere, showing the depth of 

 the chainbei-s, and a very slight cohstriction of the tube at the aperture. Traces of the 

 transvei-se strise of the surface are aLso shown. Uppei' Helderberg limestone. Columhux, 0. 



Fig. 4. A s)>ecimen in the same afsociHtion with the preceding, preserving the test ovei' the entire surface, 

 showing the regular, rounded, transvei-se stria; and the gjadually enlarging tube. 



Orthoceras varum. 



Page 289. 

 See Plate 79. 

 Fig. 5. Lateral view of a specimen, showing a common appearance of the aperture, due in part to compres- 

 sion. The shell is naturally fn.«iform, and the ohand)er of hatiitation s-omewhat gibbous- 

 Schohai-ie grit. Scfioharie, N. Y. 

 Fig. fi. A septum of the preceding, showing the transverse fiection of the lube, and the small size and cen 

 tral position of the siphuncle. i!  ? ''« 



Orthoceras Thoas. 



P.lgc 261. 



See Plates 41, 78 B, 79, 8n. 



Fig. 7. A large and very much compressed individual, showing a slight curvature of the tube, with the dis- 

 placed siphimcle, indicated by the raiseil and curved longitudinal ridge. The maceration of 

 lilt- t-hell and the destruction of the septa has probably allowed the siphuncle to fall against the 

 inlenor walls of the tube, and the extreme comjiression has shown it in i-elief on the exterior. 

 Upper Helileiberg limestone. Caledonia, N. Y. 



Fig. 8. An enlargement of the i-ui-face to three diameters, showing the sharp, continuous, longitudinal 

 ridges, and the finer ti-ansvei'se stria: crenulating their summits. Upi)er Helderberg limestone. 

 DiUilin, 0. 



Orthoceras inoptatum. 



PajfC 267. 



See Plate 87. 



Fig. 9. A fragment preserving its normal form and retaining portions of the test ovei- the surface of the 



tube. Upper Heidelberg limestone. Clarence Hollow, N. Y. 

 Fig. 10. Tlie surface of the test enlarged to three diametei-s, showing the regular longitudinal striae and the 

 more ii-regular transverse strise, with tiner intermediate lines of growth. 



