212 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



conical initial chanibei' of the shell, l)ut is perforated just above the apex l)y a large 

 foramen. 



Canilirian to Carboniferous. 



28. Actinoceras giganteum. 29. Actiuoceras insulare.* 30. Actinoceras pi-opinquum.* 



Family — Ctrtockratid.e, Chapman, 18o7. 



Longicones and Bre'S'icones with curved shell and short, often compressed l)od_y- 

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

 with an entire pei'istome. 



Genus Ctrtoceras (Goldfuss, 1832). — Shell curved, tapering rapidly (])re^•icones), 

 or more slowly (longicones) ; cross-section elliptical, ovate, or circiilar. Siphuncle 

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

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

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

 ventral side owing to the curvature of the shell. 



Cambrian to Permian. 



Suh-r/enns Meloceras (Hyatt, 1883). — Shell compi'essed, generally with a marked 

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

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

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

 towards the aperture in some species. 



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



Genus EusTHENOCERAS [Foovd, 1898). — Shell large, typically curved only in the 

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

 separated. Sutures arching upwards on the dorsal or inner curvatui'e of the shell. 

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



Carboniferous. 



33. Eusthenoceras HuUi. 34. Eustlicnoceras Bailvi. 



Fmnilij — PoTERiofERATin.E, Foord, 1888. 



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

 Sutures often oblique to longitudinal axis; siphuncle monilifoi-m, witli an oudo- 

 siplmncle in adult stage. Aperture with the peristome entire. 



