PLATE XLI. 



Okthoceras Thoas. 



rage Ml. 



Siee Plates 78 B, 79, 80, 112. 



Fig. 1. A compressed fi-agment of the outer chamber, which is more closely annulated than usual, showing 



lon^tudinal striie in some pai-ts. 

 Fig. 2. A similar sjiecimen, showing striie upon some parts of the surface. This and the preceding are 



from the limestone of the Upper Helderberg at SchoJiarie, N. T. 

 Figs. 3, 4. Specimens pi-eserving the outer chambers, which are scarcely compressed, with the annulations 



more distant than in the preceding specimens. The surface preserves the longitudinal stria. 



These specimens are from the Schohai-ie giit, and are the originals used in the description of 



0. Thoas. Schoharie, N. Y. 

 Fig. 5. The non-septate portion of a small individual, presei-ving the cylindrical form and the more frequent 



annulations, except at the upper end. From the Schoharie grit. Schoharie, N. Y. 

 Fig. 6. A large non-septate portion of a specimen retaining the natural form, and showing closely arranged 



annulations in the lower part, which gi-adually increase in distance tow^ard the apertui'e, where 



they ai-e much more distant. Schohai-ie grit. Schoharie, N. Y. 

 Fig. 7. A septate fragment with the annulations closely aiTanged, and more angular than usual. This 



specimen is the original of 0. Hyas. Schoharie gi-it. Schoharie, N. Y. 

 Fig. 8. A small uncompressed, septate portion of an individual, showing the regularity of the septa and 



annulations. From the Upper Helderberg limestone at Clarence Hollow, Eric county, N. Y. 

 Fig. 9. A fragment of a large individual referred with doubt to this species. The specimen is much com- 



pi-essed, and preserves no remains of the surface ornaments. The obli(|uity of the annulations 



is apparently due to the flattening of the shell. From the Corniferous limestone of Ohio. 



