WHITEAVES J FOSSILS OS' HAMILTON FORMATION OF ONTARIO. 407 



1-iartlett's Mills, G. Kernahan, 1894 : the two specimens figured, which 

 he has kindly presented to the Museum of the Survey. The smaller of 

 these (figs. 14 and 14 a) is an undistorted fragment fifteen millimetres in 

 length, and five mm. and a half in its greatest diameter, consisting of two 

 whole air chambers and part of a third. The distance between the pos- 

 terior septum and the one next to it, in this fragment is nearly seven mm. 

 The larger one, the original of figure 13 on the same Plate, is about forty 

 mm. in length. It is slightly but abnormally compressed, and consists 

 of eight air chambers, the four posterior ones being deep with the septa 

 widely distant, and the four anterior ones shallow with the septa com- 

 paratively near together. 



The salient features of this species would seem to be the great distance 

 of the septa apart, at a short distance from the body chamber, coupled 

 with the very slender contour of the shell, and its eccentric siphuncle. 



Bactrites (obltqueseptatus ? var.) Arkonensis. 



Plate 48, tigs. 15, 16 and 16 a. 



Cfr. Oiihnr, nix nljUqueseptntuM, G. s,nd F. %imdherger. 185,3. Verstein. Rhtinisch. 



Schichten-syst. Nassau, p. 100, pi. 18, figs. 2, 2 a-c. 

 II SdUrites oUiquesi'ptatiis, Hyatt. 1883. Genera of Fossil Cephalopoda (in Proo. 

 Boston Soo. Nat. Hist., vol. XXII.) p. 304. 



Shell resembling that of B. obliqueseptatus in (1) its small size ; (2) its 

 slightly compressed sides and consequently broadly elliptical outline in 

 transverse section ; (3) its oblique septa, as viewed laterally ; and (4) in 

 its marginal and presumably ventral siphuncle; — and differing therefrom 

 only in the circumstance that the minute sinus of each suture at the si- 

 phuncle, which Hyatt calls the ventral sinus, is not developed in the ma- 

 jority of specimens. 



Thus, out of about fifty specimens from the Hamilton formation of 

 Ontario that the writer has recently examined with a lens, only some 

 five or six have the ventral sinus distinctly developed. In all the others 

 the sutures are straight and continuous where they pass over the siphuncle. 

 Yet, in the specimen represented, enlarged four times, on Plate 48, figs. 

 16 and 16a, which consists of ten air chambers, the ventral sinus is 

 distinctly visible on each of the septa. Moreover, the Sandbergers, in 

 their original description of Bactrites, say that this sinus, which they call 

 the "dorsal lobe," and regard it, as Hyatt says, as "due to the approxima- 

 tion of the funnels to the side," is sometimes entirely wanting {"i;//flro?//,TO 

 omniiio nullus"). In their representation too (op. cit., pi. 18, fig. "2 e) of 

 the siphonal or ventral side of two of the air chambers of Orthoceras 

 ohliqueseptatum, magnified, the exposures of the siphuncle at each of the 



