270 
The American Geologist. 
Novombfr, ISW 
forniaiUiH Hall. 
f/ibbosus Hall. 
intennedius Hall. 
lodiensis Meek. 
multistnuatiix Hall. 
newberryi Hall. 
nodosuK Conrad. 
occidens Walcott. 
paralim White and VV. 
jyentalobux Hall. 
plati/stomris Hall. 
refiexus Hall. 
rictus Hall. 
spinigerus Worth en. 
subslnuosus Worthen. 
sukoplicMun Hall. 
i7ie<^■s Hall. 
nndatns Hall. 
ventricosiis Conrad. 
conicuiii Hall. 
fissureUum Hall. 
perplexum Hall. 
pyramiddtxin Hall. 
sxihpUcdtvni Meek & AV. 
acutirostre Hall. 
arcuatum Hall. 
cheiiterensc ]\Ieek and W. 
cornvforme Winchell. 
cyrtolites McChesney. 
formosum Keyes. 
lamelloHum Hall. 
subreetuhi Hall. 
tuhiforuii Hall. 
gebhnrdi Conrad. 
haliotoides M. & W. 
^(<<M.s Keyes. 
magnificuH Hall. 
muUisjnnosus Meek. 
niagarensis. Hall. 
obliquus Keyes. 
ovalis Stevens. 
parvus Swallow. 
perplicatus Hall. 
pliadilis Hall. 
retrorsus Hall. 
dnvatus Hall. 
subreetus Hall. 
sulcatum Conrad. 
symmetricus Hall. 
tribulosus White. 
undulostridtus Hall. 
IGOCERAS. 
capulus Hall. 
pabulocrinus Owen. 
plicatum Conrad. 
quincycriiic McChesney. 
DRTHONYCHIA. 
(igreste Hall. 
attenuatum Hall. 
concavum Hall. 
curvirostrum Hall. 
dentalium Hall. 
z?ici7<? Hall. 
spirale Hall. 
tortitosum Hall. 
unguiforme. Hall. 
Some of the forms included in tlie above are undoubtedly 
synonymous, l)ut they cannot be eliminated until more satisfac- 
tory material has been examined. By transferring certain appar- 
ently anomalous species to other genera, the arrangement of the 
entire group seems to l)e much more in accordance with the 
observed affinities and differences of the various species than any 
other yet suggested. And in a treatment, soon to be issued, of 
the leading forms occurring in the Mississippi basin the plan here 
proposed lias been followed. 
The oreat range of variation, even in a single species, together 
