1858.] MITRCHISON NOETHERN HIGHLANDS, ETC. 375 



^ General form very gradually tapering, with shallow close annida- 

 tions (-|-th of an inch apart in a diameter of |- of an inch) in the 

 older portion, in the young nearly smooth. Section circular. Septa 

 numerous, close-set, one to each annulation in the older part ; at a 

 diameter of 4 lines there are 15 to an inch. They are only slightly 

 concave, and bent down somewhat angularly* towards the siphuncle, 

 which is exeentric, thick, smooth-edged (not at aU beaded), and 

 compressed in a direction from front to back. It also has a shallow 

 groove along the side nearest to the centre of the shell, so as to give 

 in section a somewhat bilobed form (fig. 24 6). 



Specimens from Canada, of what I believe to be 0. multicameratum, 

 resemble this shell so strongly in the young part, and have so similar 

 a siphuncle, that it is difficult to regard them as different species ; 

 they, however, taper more suddenly. 



Oethoceeas aecuolieatum. Hall. 



(Palaeont. New York, vol. i. pi. 42. fig. 7.) 



Fragments of this species resemble those from Canada and N. 

 America, with oblique and sinuous rings-; and, though imperfect, 

 diifer decidedly from other forms accompanying them which have 

 direct annulations, and which I refer to the species next described. 



Oethoceeas veetebeale. Hall ? PL XIII. figs. 22, 23. 

 (HaU, Palgeont. New York, vol. i. pi. 43. fig. 5.) 



The specimens are much smaller than those figured by Hall, and 

 have a circular section and central siphuncle when young ; the an- 

 nulations, however, are narrower and more prominent. 



One specimen (fig. 22), with very slightly oblique rings, is com- 

 pressed ; it has blunter and broader rings than the other. None of 

 Hall's figures strictly agree with it ; but it might be the young state 

 of 0. hilineatum of that author. 



Oethoceeas uotjulosteiattim, Hall. PI. XIII. figs. 2^, 26. 

 (Pal^ont. New York, vol. i. pi. 43. fig. 7.) 



Although the side-view of Prof. Hall's figure 7 e has not the rings 

 quite so oblique as in this specimen, I do not think it a distinct 

 species, for the dorsal view quite agrees, and the rings have about 

 the same degree of convexity, with a slight keel along theii' middle, 

 more conspicuous in the weathered specimens. 



The septa appear to have a sinus on the dorsal surface like that of 

 the rings — a character quite unusual in Orthoceras. But the Cepha- 

 lopoda of this very old Silurian zone present many abnormal cha- 

 racters, such as the extraordinary size of the siphuncular tube, and 

 its being filled up with solid or cellular tabulae. One of the most 

 singular of all these shells is the species next described, and for 

 which I am obliged to institute a new genus. 



* Very much in the way that Hall represents them in his figm*e of 0. multi- 

 cameratum, op. cit. pi. 11. fig. 1 cl. 



