CLASS V 



CEPHALOPODA 



609 



Actinoceras Bronn. (Figs. 1126-1127). Orthoceracones and cyrtoceracones of usually 

 dejjressed elliptical section, Avitli large, excessively nummuloidal siphuncle. Funnels 

 very short and crumpled, sheatli almost globular. In- 

 ternal dejjosits contracting tlie central axis into an 

 annulated endosiiiliuncle with tubuli radiating from the 

 annuli. Septa often double, with an interspace between 



the two layers near the 



siphuncle, but solid near 



the shell. Ordovician 



to Carboniferous. 



Subgenera : Ormo- 



ceras Stokes (Fig. 1128). 



Fig. 1126. 



Actinoceras coMcatiim (Scliloth.). 

 Silurian ; Gotland. Abraded ' frag- 

 ment showing single septa and thick 

 annulated endosipliuncle. 1/2. 



Pig. 1127. 



Actinoceras vertcbratiim Hall. 

 Silurian ; Lockport, New York. 

 Longitudinal section showing 

 organic deposits of siphuncle 

 (alter Barrande). 



1128. 



Actinoceras (Ormoceras) hayfieldi 

 Stokes. Ordovician ; Longitudinal 

 section showing organic deposits 

 of siphuncle partly dissolved away 

 (after Stokes). 



Ordovician to Carboniferous. Par actinoceras Hyatt (Fig. 1129). Shells longer and 

 more slender than in the preceding, large siphuncular segments confined to early 



stages, and very long living chamber. Type P. (Sactoceras) 



canadense (Whiteaves). Silurian. 



Gyrt actinoceras Hyatt. Type G. (Gyrtoceras) rebelle (Barr.). 



Deiroceras Hyatt; Huronia Stokes (Fig. 1130); Discosorus 



and Gonioceras Hall. 



Fig. 1129. 



Actinocems {Parartinocerds) 

 (locens (Barr.) Silurian (E); 

 Dvoretz, Bohemia. Vertical 

 section showing senile stage 

 without organic deposits, 

 preceded by adult stage with 

 siphuncular rosettes (after 

 Ban-ande). 



Fig. 1130. 



Huronia vertehralis 

 Stokes. Ordovician ; Isle 

 Drummnnd, Lake Huron. 

 Siphuncle. 



Silurian. 



(?) Tretoceras Salter. Orthocera- 

 cones having a centren nummuloidal 

 siphuncle, similar to that of Acti- 

 noceras but smaller, and with a 

 superficial tubular siphuncle (so- 

 called), having very long but not 

 Holochoanoidal funnels. Sheath not 

 yet shown to be present. It is pos- 

 sible that the structure referred to 

 is a peripheral pseudo - siphuncle 

 formed by abnormal condition of the 

 septa. Silurian. 



II. ACTINOSIPHONATA Hyatt. 



Qrthocerctcones, 

 gyroceracones, and a 



cyrtoceracones, 



few discoidal 



nautilicones. Shells frequently breviconic, in lohich case the gerontic living chambers and 



apertures are more highly contracted than in all other Na%itiloids. Siphuncle sometimes 



empty ; organic deposits, ivhen present, in the form of laminae radiating from the sheath 



VOL. I 2 R 



