308 



tyrannus, ibid., pi. 38; Sacheri, ibid., pi. 39. Living chamber is about 

 one-half of a volution in length ; it is about three-fourths of a volution in 

 length in the type species." 



In 1894, in the "Phylogeny of an Acquired Characteristic" (Proc. 

 Amer. Philos. Soc, vol. XXXII, pp. 450 and 451) the genus is placed 

 in the new family Tarphyceratidfe, and is described as follows : 



" Barrandeoceras. 



" This genus was described in my Genera of Fossil Cephalopoda to 

 include shells having large umbilical perforations, compressed slightly 

 costated or smooth whorls. The venter usually narrower than the dorsum, 

 the whorls barely in contact or with very slight contact furrow, siphuncle 

 near but above centre, septa deeply concave, sutures having usually vent- 

 ral and dorsal saddles and lateral lobes. This last statement is true 

 of all the forms having the gyroceran mode of coiling, but not of those 

 which have the closer nautilian form. In these there is a slight dorsal 

 lobe and a different form of the paranepionic whorl which may eventually 

 lead to their generic separation. 



" The type is Barrandeoceras (Naut.) natator, sp. Billings." 



Eight species of this genus are enumerated or described by Hyatt in 

 the " Phylogeny," two from the Cambro-Silurian rocks of the Province of 

 Quebec, one from the same formation in the State of New York, four from 

 the Silurian rocks of Bohemia, and one from the Niagara group of Indiana. 



At present (1906) four species of Barrandeoceras have been recognized 

 as occurring in Canada, two in the Chazy, and two in the Black River lime- 

 stone. 



These are as follows : 



(1.) Barrandeoceras natator, Billings. (Sp.) 

 Plate 39, figs. 1, la, and 16. 



Nautilu» natator, Billings 1859. Canad. Nat., vol. IV, p. 466. 



Barrandeoceras Tiatator, Hyatt 1883. Proc. Boston Soo. Nat. Hist., vol. 



XXII, p. 299 ; and (1894) Proc. Amer. Phil. 



Soc, vol. XXXII, p. 452. 



Original description of Nautilus natator. "Discoid planorbiform, all 

 the whorls exposed in the umbilicus. Tube slender, gradually increasing 

 in size, so that on the completion of the fifth whorl the diameter of the 

 coil is four and one fourth inches. Section oval, the dorso-ventral dia- 

 meter being greater than the lateral in the proportion of about 8 to 6 (?) 

 Septa at the end of fourth whorl, three in about seven lines, measured on 

 the side. Surface and siphuncle unknown. 



