TROCHOCERATI D^. 
41 
by its curvature that the diameter of the discoidal spire was four 
inches and a half nearly. 
“This species is closely allied to Lituites (TrocTioceras) giganteiis, 
Sowerby, but differs in its more round dorsal aspect, and in the 
annulations being extended quite across . . . 
“ Formation and Locality. — Upper Siluidan, Port Daniel, Gaspe 
[Lower Canada].” {Billings.) 
BemarTcs. The specimen which I have referred to BiUings’s species 
is a fragment, apparently of the body-chamber, as no septa are 
visible. It is very distinctly cyhndrical in section, the ratio of the 
dorso-ventral to the transverse diameter being as 25:21. The 
annulations are very strong and completely encircle the shell, form- 
ing a deep and narrow sinus upon the flat ventral side. They are 
about 7 lines distant from each other at the thickest part of the 
fossil, where the dorso-ventral diameter is 2 inches. Traces of fine 
longitudinal lines are visible in one part of the shell, but the sur- 
face is everywhere much eroded, and nothing is seen of the coarse 
transverse striae described by Billings. 
The dimensions of the British Museum example are the follow- 
ing : — Length, measured along the outer curvature, 8 inches ; the 
same, inner curvature, 3 inches 10 lines ; greatest diameter (dorso- 
ventral), 2 inches ; least, 1 inch 4 lines. 
Horizon. Niagara Group (\Yenlock). 
Locality. Wabash, Indiana. 
Trochoceras Halli, Foord. 
1847. Lituites undatus, Hall, Palaeontology of New York, vol. i. p, 52, 
pi. xiii. ff. 1 a, 1 6, 2 a? (excl. ff. 2, 3, also pi. xiii. (bis) f 1). 
1857. Lituites undatus. Chapman, Annals & Magazine Nat. Hist. 
2nd series, vol. xx. p. 117. 
1863. Lituites undatus, Billings, in Logan’s Geol. of Canada, p. 156, 
and Appendix, p. 951. 
1883. Trocholites undatus (pars), Hyatt, Proc. Boston Soc. Nat. Hist, 
vol. xxii. p. 267. 
Bp. Char. The shell, which is not complete, consists of two 
volutions ; the asymmetry is slight, but quite discernible. The 
shell increases its diameter about three times in the last volution. 
The section is distinctly subquadrate, the ventral side being the 
broadest, as well as being considerably fiattened. The surface is 
ornamented with oblique, rounded, not very prominent annulations, 
divided by concave interspaces of about equal width. The annula- 
tions bend backwards on the ventral side, and there form a deep 
sinus ; while on the dorsal or concave side, approaching the um- 
