I20 



The Ottawa Naturalist. [October 



1898, Professor Hyatt expressed the following opinion in regard 

 to Trochoceras Halli : " Foord's species is clearly in my opinion 

 a species of Sphyradoceras, in which 1 now include also my g^enera 

 Peismoceras and Systrophoceras. This genus and Plectoceras are 

 now close allies and appear together in my MS. of the article 

 Cephalopoda in Eastman's translation of Zittel's Text-book of 

 Palaeontology, under the family name Plectoceratidae. What you 

 say about the siphuncle being ventrad of center, etc., if your speci- 

 mens are also heavily annulated from a comparatively early stage 

 and trochoceran in form, or even if comparatively symmetrical, 

 seems to me to place them better in in Sphyradoceras.''' Yet, in 

 the printed text of that article, which embodies Hyatt's latest views 

 on the Cephalopoda, Plectoceras is said to be Ordovician, Silurian 

 and gyroceraconic, and Sphyradoceras Silurian, Devonian and 

 " almost exclusively torticonic of the trochoceran type." 



If Trochoceras Halli \s a Plectoceras, there are at least two 

 Canadian species of that genus, whose synonymy is as follows : 

 Plectocbras Jason (Billings). 



Nautilus Jasoti, Billings. 1859. Canad Nai. and Geol., vol. iv, p. 464. 

 Plectoceras Jason, Hyatt. 1883. Proc. Boston See. Nat Hist., vol. xxii, p. 

 268; and (1894) Proc. Amer. Philos. Soc, vol. xxxii, p. 498. 

 Types : three specimens in the Museum of the Geological 

 Survey of Canada, that were collected by Sir W. E. Logan and 

 James Richardson in 1856, from the " Chazy limestone'" (not the 

 Calciferous, as stated by Hyatt) of the Mingan Islands. 



Plectoceras Halli (Foord). 



Litiutes undatus, Hall, pars. 1847. Palffiont. N. York, vol. i, pi. XHI, figs. 



irt and \b [cant. excL). 

 Trochoceras Haiti, Foord. 1861. Cat. Foss. Cephal. Brit. Mus., pt. ii, p. 41, 



and p. 4a, figs. 4 a, b. 

 Types : two specimens in the British Museum, from the Black 

 River limestone at Lorette. Similar specimens in the Museum of 

 the Survey are from Lorette and other localities in the Province of 

 Quebec, as previously stated, and Mr. Walter R. Billings has found 

 a specimen that seems to be referable to this species in rocks ot 

 the same age near Ottawa city. 



The brief description of P. obscurum, Hyatt, unaccompanied 



