CEPHALOPODA. 303 



In its surface-markings this species closely resembles 0. nuntium and 0. cro- 

 talum, but the annulations are much more abrupt and frequent. In its rate of 

 enlargement and general appearance it is very similar to 0. lima. The annula- 

 tions are nearly as frequent, being slightly more numerous in that species ; but 

 the surface characters are very distinct. This form was doubtfully identified 

 with young individuals of 0. perekgans, Salter,* from the Silurian of England 

 — a species which is characterized by fine transverse striae, without longitu- 

 dinal lines and with the annulations subacute. 0. solitarium, Barrande, from 

 the Silurian of Bohemia, presents surface ornaments which cannot be distin- 

 guished from this species, but is otherwise very different; that one having 

 narrow, sharp furrows, with rounded, curving annulations. 0. Ibex, Sowerby, 

 from the same horizon as 0. perekgans, is very similar, with the addition of 

 distinct, longitudinal striae. The form here described is removed from the last 

 two species by the more rapidly expanding cone, abrupt annulations, and the 

 flat, interannular spaces. 



Formation and locality. In the shales of the Hamilton" group at Moscow, N. Y. 



Orthoceras lima, n. sp. 



PLATE CXIII, FIGS. 24, 25. 



Shell straight, very gradually enlarging. The chamber of habitation, septa 

 and siphuncle are unknown. 



Air-chambers regular, having a depth equal to the distance between the 

 annulations, or from I to 1.5 mm. Suture lines straight and horizontal in 

 the furrows between the annulations.- 



Test not preserved. Tube ornamented by very numerous, regular, sharp 

 annulations, with the intermediate furrows regularly concave. There are 

 from eight to ten annulations in the length of ten mm. Surfice-markings, 

 as preserved on the internal mould, are very fine, longitudinal stria?, inter- 

 rupted by lines of growth between the annulations. 



* Orthocerag perelegans, Salter. Memoirs of the Geological Survey of Great Britain : vol. ii, part i, p. 354, 

 pi. 13, tigs. 2-4. 1848. 



