482 G. C. Crick — Orthocerata from North China. 



bande e^, which is regarded as the equivalent of the Wenlock and 

 Ludlow of this country (see Fig. 1). In that species the siphuncular 

 elements decrease in diameter towards the body -chamber.^ They 

 appear to do the same in the present specimen, but this, I think, 

 ia due to the fact that the anterior part of the specimen is 

 weathered down further from the median axis than the posterior part. 



Fig. 1. — Longitudinal section of Actinoceras {Taractinoceras) docens, J. Barrande, 

 sp. a, a, organic deposits upon the necks, of the septa, forming obstruction 

 rings [anneaux ohstructeurs). Silurian (Etage E, bande e-i) ■ Dworetz, 

 Bohemia. (After Foord.) 



The specimen may, I think, safely be referred to Stokes's genus 

 Ormoceras," a genus confined to the Ordovician rocks of North 

 America and now regarded as a subgenus of Actinoceras ; ^ and 

 I would suggest that it is nearly allied to Hall's Ormoceras tenuijilum,* 



1 Foord (Cat. Foss. Ceph. British Museum, pt. i, 1888, p. 208, fig. 32) referred 

 Barrande's species to Hyatt's genus Sacioceras (Proc. Boston Soc. Nat. Hist., 

 vol. xxii, 1883, p. 273), but Hyatt himself, in Eastmann's translation of Zittel's 

 " Textbook of Paleontology " (p. 528, fig. 1080), refers the species to Far actinoceras, 

 a new subgenus of Actinoceras. 



2 C. Stokes: Trans. Geol. Soc. [2], vol. v, pt. 3 (1840), p. 709. 



2 A. Hyatt in Eastmann's Translation of Zittel's "Textbook of Palaeontology," 

 vol. i (1900), p. 528. 



* J. Hall': Nat. Hist. New York, pt. vi, Pala3ontology, vol. i (1848), p. 55, pi. xv, 

 figs, la-c; pi. xvi, figs. la-e\ pi. xvii, figs, la, b. See also J. Barrande: Syst. 

 Sil. Boheme, vol. ii, pi. ccxxxvii, figs. 5-7. 



