518 
MOLLUSCA SUB-KINGDOM VI 
Orthoceras, Breyn (Figs. 1060, 1061). Long tapering orthoceracones and cyrto- 



Fic. 1060. 
Orthoceras intermedium, Marklin. Silurian; Barr. Silurian; Kozorz, 
Gottland. Longitudinal section showing Bohemia. Longitudinal 
siphuncle, septa, and pseudosepta ; camerae section showing short 
filled up with calcite. 
ceracones, smooth, or with only transverse striae and growth 
bands. Siphuncle generally larger than in Geisonoceras, centren 
or slightly dorsad 
about the funnels as in Annulosiphonata. Silurian to Trias. 

Fic. 1063. 
Dawsonoceras an nula- 
tum, Sowb. sp. Silurian 
(E);  Viscocilka, Bo- 
hemia. Terminal por- 
tion showing shell o 
living chamber and 
sectioned camerae (after 
Barrande). 









Fic. 1061. 
Orthoceras Michelini, 
siphonal funnels. 
of centre. Deposits when present gathered 
Geisonoceras, Hyatt (Fig. 1062). Similar 
to the last, but sides spreading more rapidly, 

and siphuncle empty, centren, or slightly Fic. 1062. 
ventrad of centre. Ordovician to Carbon- — Geisonoceras timidwm, 
“fp ta ~ Si ria . ly = 
iferous. Barr. sp. Silurian; Loch 
kow, Bohemia. 
Protobactrites, gen. noy. Long pencil- 
shaped orthoceracones and cyrtoceracones, circular or compressed 
elliptical in section, ornamented with transverse and sometimes 
longitudinal striae. Siphuncle tubular, centren or near the centre. 
Truncation occurs in some species, and others are more or less 
transitional to Bactrites among the Ammonoids. Type P. (Orth.) 
styloideum, Barr. sp. Silurian to Carboniferous. 
Family 2. Cycloceratidae. 
Orthoceracones and cyrtoceracones having annuli with transverse 
striae or bands of growth at all stages; longitudinal ridges, when 
present, more or less discontinuous. The earliest forms often have 
large siphuncles, and are apparently more directly connected with 
primitive Endoceratida than with Orthoceratidae. 
Protocycloceras, gen. nov. Annulated orthoceracones and cyrto- 
ceracones without longitudinal ridges. Siphunele large. Type P. 
(Orth.) Lamarcki, Bill. sp. Ordovician. 
Cycloceras, M‘Coy (Dietyoceras, Heloceras, Eichw.). Annu- 
lated orthoceracones and cyrtoceracones with discontinuous longi- 
tudinal ridges. Siphuncle generally tubular or with fusiform 
; Segments; deposits when present irregular as in Orthoceras. 
Annuli often become obsolete in paragerontic stages. Ordovician 
to Permian. 
Dawsonoceras, Hyatt (Fig. 1063). Similar to Cyeloceras, but 
having prominent frilled bands of growth between and on the annulations, the frills 
