GENUS ACTINOCERAS. 21 J 



Sub-group Moniliformes. (Sjiecies with moniliform siphuncle.) 

 14. Orthoceras Hindei.* 15. Orthoceras subclavatum.* 16. Orthoceras pilum* 



II. Group Annulata. (Species with transverse annulations.) 

 17. Orthoceras lsevigatum. 



III. Group Angulata. (Species with longitudinal ridges.) 

 18. Orthoceras Wriglitii. 



IV. Group Lineata. (Species with fine transverse or longitudinal lines.) 



19. Orthoceras Kildarense.* 21. Orthoceras Hihernicum.* 



20. „ salvum. 22. „ pulcherrimum.* 



V. Group Imbricata. (Species with imbricating stripe.) 



23. Orthoceras Clauense.* 25. Orthoceras multistriatum.* 



24. „ Sollasi.* 26. „ perellipticum.* 



b. Brevicones. 

 27. Orthoceras perconicum.* 



Family — Actinoceeatid.e, Saeraann, 1854. 



Longicones and Brevicones with large nummuloidal siphnnele, and endo- 

 siphuncle ; the latter usually with calcareous deposits, and connected by tnbnli with 

 the wall of the siphnnele. 



Genus Actinoceras (Bronn, 1837). -Shell straight, elongate-conical j cross-section 

 circular to subcircular. Septa usually more arcuate 1 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 

 \v;ill and gives off at intervals a number of radiating canals or tubuli which reach 

 and penetrate the wall of the siphuncle. The siphuncle forms, as in Wndoceras, the 



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