212 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



conical initial chamber of the shell, bnt is perforated just above the apex by a large 

 foramen. 



Cambrian to Carboniferous. 



28. Actinoceras giganteum. 29. Actinoceras insulare.* 30. Actinoceras propinquum.* 



Family — Cyrtooeeatidje, Chapman, 1857. 



Longicones and Brevicones with curved shell and short, often compressed body- 

 chamber. Siphuncle nnmmnloidal, usually filled with radiating deposits. Aperture 

 w T ith an entire peristome. 



Genus Cyetoceras (Groldfuss, 1832). — Shell curved, tapering rapidly (brevicones), 

 or more slowly (longicones) ; cross-section elliptical, ovate, or circular. Siphnncle 

 moderately large, nummuloidal, generally situated near the convex (ventral) curva- 

 ture of the shell, usually with well-developed radiating deposits or obstruction- 

 rings. Body-chamber short ; aperture simple. Septa greatly elevated towards the 

 ventral side owing to the curvature of the shell. 



Cambrian to Permian. 



Sub-genus Meloceeas (Hyatt, 1883).— Shell compressed, generally with a marked 

 curvature only in the apical region. Section broadly ovate to elliptical. Siphnncle 

 nnmmnloidal, external (exogastric), internal (endogastric), or, more rarely, sub- 

 central (mediogastric). Body-chamber usually short, with a tendency to contraction 

 towards the aperture in some species. 



31. Cyrtoceras (Meloceras) apicale.* 32. Cyrtoceras (Meloceras) arcuatoseptatum.* 



Genus Eusthenoceeas (Foord, 1898). — Shell large, typically curved only in the 

 apical portion. Septa at first approximate, afterwards becoming very widely 

 separated. Sutures arching upwards on the dorsal or inner curvature of the shell. 

 Siphuncle subcentral in the direction of the ventral region, apparently cylindrical. 



Carboniferous. 



33. Eusthenoceras Hnlli. 34. Eusthenoceras Bailyi. 



Family — Poteeioceeatidje, Foord, 1888. 



Fusiform, slightly curved shells, inflated in the middle, with slender apex. 

 Sutures often oblique to longitudinal axis ; siphuncle moniliform, with an endo- 

 siphnncle in adult stage. Aperture with the peristome entire. 



