1904] The Canadian Species of Trocholites. 13 



THE CANADIAN SPECIES OF TROCHOLITES. 



By J. F. Whiteaves. 



From the dismemberment and reconstruction of so many of 

 the older genera ot nautiloid shells of the Cambro-Silurian and 

 Silurian rocks, which the progress of modern research has 

 necessitated, the genus Trocholites has emerged unscathed. 



First described by Conrad in 1838 and again in 1842, it has 

 since been studied, described more fully, and illustrated, by Hall, 

 Foord, Schroder, Holm and Hyatt. 



The original description of the genus in 1838, on page 118 of 

 the Second Annual Geological Report of the State of New York, 

 is as follows : " Shell in the form of an Ammonite ; volutions con- 

 tiguous, gradually increasing in diameter ; septa plain." And, 

 the additional definition of the genus, in 1842, on page 274 of the 

 eighth volume of the Journal of the Academy of Natural Sciences 

 of Philadelphia, is in these words: "Involute; symmetrical ; 

 whirls contiguous ; the back of inner volutions rounded, fitting 

 into a corresponding groove ; septa convex ; siphuncle near the 

 inner margin." "This genus," Conrad adds, "differs from 

 Lituites in having a submarginal siphuncle, and in not being ex- 

 tended into a straight or bent prolongation. The aperture is 

 widely different, being of a lunate outline, whilst in Lituites it is 

 nearly round." As now understood, shells of the genus Trocholites 

 may be roughly described as small nautilicones, with slender 

 whorls that are compressed on the venter and dorsum and ex- 

 panded at the sides, their outline in cross section being usually 

 reniform. The surface markings consist of small flexuous trans- 

 verse ribs, ridges or stria, often accompanied with spiral raised 

 lines. The sutures of the septa are also flexuous ; the siphuncle 

 of the adult shell is placed near the dorsum, or at least on the 

 inner side of the centre ; and the chamber of habitation occupies 

 from rather less than one-half to about three-quarters of the outer 

 volution. 



In the Guelph formation of Ontario there is a fossil that seems 

 to be identical with the Lituites multicostatus of Whitfield (1882) 

 which Hyatt says is synonymous with the L. Graftonensis of Meek 

 and Worthen (1870), though it does not belong to the genus 



