PLATE XIX. 

 Orthoceras crbbescbns, Hall. 



Page il3. 



Fig. 1. View of a large specimen, preserving the outer chamber and several of the septa; the 



lower end showing the depth of the septa. 

 " 2. View of another individual, having part of the septa in the lower end removed, and 



exposing the siphuncle. 

 " 3. A smaller individual, which preserves traces of the longitudinal ridges. 



Orthoceras colvmnare, Hall. 



Page 411. 



Fig. 4. A fragment preserving the filling of four chambers, which are very distant. 

 " 5. A transverse section of the lower end of the preceding specimen. 

 " 6. View of another specimen, preserving nine chambers, which are very irregular in their 



distances. In the upper part there is a small piece of the shell represented, showing 



the surface characters. 

 " 8. A fragment of this species of smaller size, preserving essentially the same characters. 



Orthoceras loxias. Hall. 



Page 416. 



Fig. 7. Figure of specimen of natural size, preserving about seventeen of the septa, with the shell 

 partially preserved, or replaced by mineral matter on the other parts of the surface. 

 This species is not positively known in the Niagara limestone, and should therefore 

 have been omitted from the index of the fossils of the Niagara group. 



Orthoceras angulatcx, Wahl. 



Page 413. 



Fig. 9. A fragment of this species of about six inches in length, preserving above twenty septa 

 and a part of the chamber of habitation; from Racine, Wisconsin. 

 " 10. From an impression of the exterior of a specimen similar to fig. 9, and from the same 



locality. 

 " 11. From an impression of the exterior of a similar form, from Bridgeport, Illinois. The 

 specimen, at a point where it is one inch and five-eighths in diameter, preserves above 

 twenty longitudinal ridges in the semi-circumference, giving more than forty in the 

 entire circumference. The character of surface in these impressions is precisely like 

 that of 0. cancellatiim. Hall, from the Niagara group of New York, and differs in 

 ' no essential particular from the minute surface markings of O. columnare. 



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