406 CONTEIBUTIONS TO CANADIAN PALEONTOLOGY. 



The name of Orthoceras e:eile, Hall, was included in a previous list of the 

 fossils of this formation and province on the strength of a statement by 

 Professor H. A. Nicholson, that " fragments of a slender Ortlujceras which 

 appear to belong to this species, are not rare in the Hamilton formation 

 at Widder.'' The writer has not seen any of the specimens upon which 

 this opinion was based, but most of the small Orthocerata from 

 Thedford and Bartlett's Mills in the Museum of the Survey that 

 have been loaned, for comparison, by local collectors, except those here 

 referred to Bactrites, seem to agree better with Hall's latest descrip- 

 tion and figures of 0. suhulatum than with those of 0. e.rile. Tn the re- 

 marks which follow the latest description of 0. e.vile it is stated that it 

 differs from 0. constrictum and 0. suhuhUuni in its excentric siphuncle 

 and more distant septa. The air chambers of 0. e.rile, too, are described 

 as " increasing in depth towards the outer chamber," and as " varying 

 from two or three mm., to five mm., in the length of 100 mm., or about 

 thirty chambers." With the exception of the Baiirili'S and of the two 

 specimens here described as 0. Arkonense, all the small Orthocerata from 

 Thedford and Bartlett's Mills that the writer has seen, have a central or 

 very nearly central siphuncle, about one millimetre in diameter. Some 

 of them are crushed nearly flat, but othei'S, which are undistorted, are 

 circular in transverse section. The depth of the air chambers and conse- 

 quent distance of the sutures apart, varies from as little as one millimetre 

 throughout, to two or even three millimetres, in different specimens, 

 though it is by no means certain that all these belong to the same species. 

 However that may be, in this respect also they seem to agree better with 

 the description of 0. subulatum than with that of 0. e.r.ile. 



B. 2. Sipliuncle eccentric. 



Orthoceras exile (Hall) Nicholson. 



Orthorrrns i.nle (Hall) Nicholson. 1S75. Rep. Pal. Prov. Ontario, p. SX 



Widder, Nicholson {op. cit.). See the remarks on the preceding 

 species. 



Orthoceras Arkonense. (N. Sp.) 

 Plate 48, figs. 13, 14 and 14 a. 



Shell slender, longicone, almost cylindrical, but slightly compressed, so 

 that the outline of a transverse section is broadly elliptical : air chambers, 

 except the three or four next to the chamber of habitation, so deep that 

 the distance between the sutures is greater than the maximum diameter 

 of the tube ; siphuncle eccentric, only oljserved at the septa. Surface 

 markings unknown. 



