198 
AUG. F. FOERSTE 
referred to the genera Cyclostomiceras, Cyrtocerina, and Mae- 
lonoceras, but the Canadian species so referred belong to dif- 
ferent genera from those occurring in later strata. In typical 
Cyclostomiceras , of Canadian age, the segments of the siphuncle 
present concave vertical outlines, while the Niagaran species 
Cyrtoeras hrevicorne Hall and Cyrtoceras orodes Billings, re- 
ferred by Grabau and Shimer to Cyclostomiceras, belong to a 
distinct genus with short septal necks and convex connecting 
rings, for which the term Amp hicyrtoc eras is proposed on the 
following pages. Cyrtoceidna typica Billings, from the Black 
River, has nummuloidal segments in the siphuncle (Plate XLI, 
Fig. 9) while in Cyrtoce^dna mercurius Billings these segments 
present concave vertical outlines (Plate XLI, Fig. 8) as in Clark- 
oceras, a genus which seems to be confined to the Canadian. In 
Maelonoceras praematurum (Billings), from the Black River, 
the segments of the siphuncle are subfusiform, while in Cyrto- 
ceras metellus Billings, from the Canadian, these segments are 
strongly nummuloidal in form, if specimen No. 820a in the Vic- 
toria Memorial Museum correctly represents this species. 
Such genera as Eremoceras and Piloceras are confined to the 
Canadian. In both, the segments of the siphuncle have concave 
vertical outlines within the camerae. 
Concave vertical outlines are presented also by a considerable ^ 
number of those orthoconic shells which were described by Bill- 
ings and others from Canadian strata under the generic term 
Orthoceras. In fact, all of the Canadian orthoconic species, con- 
cerning which it has been possible to learn the structure of the 
siphuncle, have siphuncular segments with concave vertical out- 
lines. Of these, the annulated forms are, at present, referred to 
Pj^otocycloceras. Possibly most of the smooth forms will fall 
under Ellesmereoceras.^ They are characterized, as a rule, by 
rather closely arranged septa and by siphuncles of more moderate 
size than in typical Eiidoceras. Orthoconic specimens, with 
siphuncles more readily comparable with those of typical En- 
doceras, also exist in Canadian strata. In none of the Canadian 
Endoceroid specimens described by Billings has it been possible 
to discover the presence of endocones. From this it does not 
follow necessarily that endocones are absent, since the actual 
® Foerste, A. F., Notes on Arctic Ordovician and Silurian cephalopods; 
Journ. Sci. Lab. Denison Univ., vol. 19, p. 265, pi. 27, figs. 3A, B, C; pi. 33, 
fig. 3, 1921. 
