262 PALAEONTOLOGY OF NEW Y011K. 



longitudinal striae. Most of the specimens from the grit preserve only traces 

 of the latter. 



The internal mould is smooth, with the exception of the annulations. 

 The septal sutures are in the furrows between the annulations, and are but 

 slightly impressed. 



The largest fragment referred to this species has a length of 170 mm., 

 with diameters of forty and twenty-seven mm. respectively, at the two 

 extremities, and showing twenty-eight of the annulations in its entire 

 length. Another example has nineteen annulations in the length of eighty- 

 eight mm. 



This species is associated with 0. multicinctum, and may be distinguished 

 from it by the more gradual enlargement of the tube, greater distance between 

 the septa and annulations, and the concavity of the septa. It differs from 

 0. crotalum, of the Hamilton group, in the coincidence of the furrows and 

 the septa, their horizontal position with regard to the longitudinal axis of the 

 shell, the apical angle, and the coarser surface-markings. 



Owing to the great variation in the frequency of the annulations, and the 

 fragmentary condition of the examples, this species was originally described as 

 O. Thoas, to include those with distant annulations, and 0. Hyas, embracing 

 the forms ornamented with more frequent annulations. The discovery of 

 specimens such as fig. 6, pi. 41, and fig. 5, pi. 78 B, show the variation to which 

 the annulations are subject on the same individual, and the specific identity of 

 the various fragments. 



This is probably the species indicated by M. F. de Castelnau (Essai sur le 

 Sysieme Silurien de V Aml-rique Septentrionale : Paris, 1843), as Huronia Stokesi, 

 and cited as occurring in the calcareous schists at Schoharie, N. Y. The 

 evidently erroneous locality references, for many of the fossils, imperfectly 

 figured in the above work, render any changes in the nomenclature of the 

 present recognized species undesirable without farther knowledge. 



In its vertical distribution this species is known to occur in the Schoharie 

 grit, in the limestone immediately above, and the Upper Helderberg limestones 



