( KI'll Al.i'IlM'A 

 A.-lln.p,--r. bin-. 1 



Family ACTINOCERATID 1 



ii- ACTINOCEKAS. Brnnn. ls:{7 

 iN'n'KRAR Blt;-MVi >'//<, 1840. 



I'l.ATE XI. VII FKiS. I*-IT. 



iiaefnu bigtbfi STOKBM. 1840. Tran*. Qeolog. Soc. London, MC. or , vol. \, p. 707, (tlif. in <llit<>, 



v,,l I, p| xxv, figs. 13. 1824). 



<'"in|ar> (frmocerat r>mii>'/. \\ M.I . PalaNtntoloffy of New Ynrlc, v,.l. I p. R5, pi. xv. lit;. 1 lr; pi. xvi. 

 rigs. 1-1; pi. xvit, flg8. la. '. 



Considerable uncertainty must long remain in regard to the specific values of 

 the various orthoceran shells illustrated by Bigsby in 1824 and obtained from 

 Thessalon and other islands in lake Huron.' Of the several plates of illustrations 

 representing these, names were given only to the Huronias ami those by Stokes. It 

 was only with the publication of Stokes' paper, cited above, that names were pro- 

 posed for some, but not all of the examples of .!.//' /I/KV/-./V figured by Bigsby. All of 

 these are weathered interiors, and there is an evident agreement among them all, 

 including also those referred to the genus Ormoceras, notwithstanding the fact that 

 later investigations have tended to indicate a more recent age to the species there 

 termed Ormocerns backi and 0. buyfieldi. Actinoceras bigsbyi is safely enough an early 

 Trenton form, with many evident points of relationship to Hormoceras lenuifilum 

 Hull, of the Black River limestone of New York. The two are undoubtedly conge- 

 neric, though the New York specimens are not often retained in such a manner as to 

 show the endosiphon and its radial canals. 



The Minnesota collections have furnished but two or three specimens which 

 may l>e referred to this species, one exposing in vertical section twelve air-chambers 

 in a length of 105 mm., with a width at the upper end of 36 mm. and at the lower 

 end of 25 mm. The other specimen consists of an internal cast of four air-chambers, 

 showing that the sipho is very large and excentric, extending quite to the margin. 

 The great width, however, is at the lower surface of each air-chamber, its diameter 

 greatly diminishing at the upper surface. The greatest width of the siphonal beads. 

 extending thus into the chambers and resting with a broad base upon the septa, is 

 fully two-thirds the diameter of the shell. The endosiphonal walls are thick 

 especially where the beads are broadest, and the endosiphon seems to vary ID 

 with its position in the shell. The casts of this tube show a wrinkled surface and 

 bases of radial branches. 



Formation and locality. \n the Ttvtmm liin.Ktun.- at Mlnin-apnlK and at (Jarrli-k'i -(UArry, Dear 

 Rochester, Minnesota. 



Muteum Rrgutrr. No. 23, IM. 



Thr till.- of Hlf-tijr'. pap- N ! on th Onfr*ph)r nd Oeobwy of !.. Trn . U- <!. I. pp 



m -. 



