GENUS ACTINOCERAS. 211 



Sub-group Moniliformes. {Sjiecies with moniUform nljjJtnncle.) 

 14. Ortlioceras HinJei.* 15. Orthoceras subclavatuni.* 10. Ortlioceras pilum.* 



II. Group Annulata. {Species tvith transverse annulafions.) 

 17. Ortliot'ovas loovi^atnin. 



III. Group Anoulata. {Species with loiujitiidinal rid(jes.) 

 18. Ortlidceras Wriglitii. 



IV. Group LiNEATA. {Species with fine transverse or longitudinal lines.) 



19. Ortlioceras Kiklaronse.* 21. Ortlioforas Hiheniicuin.* 



20. ,, sahnini. 22. ., ]iiilcliciTiiiuiiii.* 



V. Gronj) Imbkicata. {Sjjecies with imhricatinij striiv.) 



23. Ortlioceras Clanense.* 25. Orthoceras multistriatuin.* 



24. „ SoUasi.* 26. „ perelliptieiiin.* 



B. BUEVICONES. 



27. Ortlioceras perc(jiiicuiii.* 



Family — AcTixorERATiD.K, Saemann, 1 854. 



Longiconcs and Breviconos with larg-c niiiiniiulnidnl si|)liuncl(', and ciido- 

 siphunclc ; the hitter usually with calcni'oous depo.sits, and comicctL'd liy tuliuli witli 

 the wall of the siphuncle. 



(t«3hw6" AcTixocEif.\s {Bromi, 1837). — Shell straight, elongate-conical; cross-section 

 circular to snbcircular. Septa usually more arcuate than in Orthoceras; necks 

 (funnels) very short. Siphuncle very large, the diameter sometimes amounting to 

 half that of the shell ; much inflated between the septa, forming a series of segments 

 of a compressed-globular shape, with calcareous wall ; often contracted by crystalline 

 deposits secreted about the necks ("anneaux obstructeurs" of Barrande). Between 

 these deposits runs longitudinally the endosiphuncle (prosipho), which has a distinct 

 wall and gives off at intervals a number of radiating canals or tubuli which reach 

 and jienetrate the wall of the siphuncle. The siphuncle forms, as in Kiidoceras, the 



