CYETOCEEATID^. 
271 
1859. Cyrtoceras falx, Salter, Canadian Organic Remains, e . i. p. 32, 
pi. yii. ff. 1-4. 
1863. Cyrtoceras falx , Billings, Geol. of Canada, Appendix, p. 951. 
Bp. Char. “Laterally compressed, section an ellipse, somewhat 
acuminated at either end ; diameters as 7 to 10 ; sides broadly 
convex ; dorsal and ventral aspects more acutely rounded than the 
sides ; septa much arched in the direction from the ventral to the 
dorsal aspects ; in crossing the latter they are strongly undulated 
towards the aperture ; siphuncle small, dorsal [external] ; general 
curvature very slight near the oral extremity, but amounting to 
more than | of a whorl in the last two inches in length of the small 
end. The specimens examined do not show the distance of the 
septa. The surface of the shell appears to have been striated 
transversely. A specimen which measures 3 inches in length 
along the outside curve tapers from 10 lines to 3 in the dorso- 
ventral diameter, and from 7^ to 2^ lines in the lateral diameters. 
“ Fragments of this species cannot well be distinguished from 
those of C. simplex, unless by attention to the form of the section, 
which in this species is about equally narrowed at either end, while 
in G. simplex it is more rounded on the ventral than on the dorsal 
aspect.” (Billinys.) 
Eemarlcs. To Billings’s description of this species it may be added 
that Salter describes the septa as being “ close, concave from back to 
front.” He compares C. falx with C. macrostomum, C. arcuatum, 
and C. camurum, HaU, but recognizes the fact that these all have 
more distant septa. 
Horizon. Black River (= Llandeilo Limestones?). 
Locality. Allumettes Island, River Ottawa, Canada. 
Represented by two imperfect specimens, transferred from the 
Museum of Practical Geology. 
Cyrtoceras (Meloceras) centrifugum, Salter, sp. 
1865. Cyrtoceras centrifugum, Salter, in Strachey’s Palaeont. of Niti in 
the Northern Himalaya, &c. p. 13, pi. ii. f. 1. 
B)o. Char. “ Slightly curved, ventricose (contracted toward the 
last chamber ?), the section not much compressed laterally, broad, 
oval, 17 lines by 13, the siphon quite external. The septa are 
rather close [?] and concave ; considerably arched backwards (but 
not oblique) on the sides, and therefore projecting forwards on the 
ventral and dorsal aspects. Last chamber ? . . .” 
“ The sheR is slightly curved, very conical from its rapid tapering, 
and appears to be contracted towards the last chamber. The section 
is regularly broad-oval ; the siphuncle quite external and rather 
