128 The Amct'icdn Geolof/isf. February, 1895 
sct'in lo inc to very siil>staiiliiillv slrciiiithcii IfviUt's ooiici'ptioii of llie 
common straijilil orllioccraii aiu-i'sloror botli iiauliloids and ammonoids, 
and there is no closer approximation lo. or e\i)ressioM of, this radicle 
tliiin in the nauliloid slu'llsof the Lower Silurian wiiieh 1 havr rt-cetitly 
termed ]\'((>iiio. 
In regard to tliis genus, Xtiti/io. 1 may venture to say on my own be- 
lialf to my various kindly reviewers that in Ihe brief and i)reliminary 
descrii)tii)n of the Minneai)()lis sliells I did not believe myself to bo ig- 
noring the work of Holm upon similar shells which he referred to Mn- 
doccviis, knowing that the (H)]jortunity wt)uid soon be afforded of do- 
ing it fuller justice in a more lengthy account of the Minnesota Silurian 
cephalopods, and I am sorry if offense has been given i)y my apparent 
omission. Nonno (oiUniKi: none will, at least, deny its euphony, and to 
the suggestion in the December number of this journal that the luime 
is inappropriate to a genus of cephalo[)ods, it may be remarked that 
the good old terms Loliga and Sepia are [)leasingly discordant with the 
recent spondaic terminology of the.se creatures. No one familiar witli 
the structure of typical Kiidorcrris will long stand out for the gen(>ric 
identity of the two. I>ut what i)lace is there for X<i)nii> in ])r. Itather's 
two-fold division of the ("ephalopoda: (he •'Lipo-proloconchia"' ;iiul the 
'• Sosi-|)rotoconchia;'" the former •• jjract ically coextensive with the 
Xautiloidea." "whicli. starling with a very fragile [irotoconch. soon 
lost it altogether." the lalli'r. '-starting with a stouter protoconch"" and 
preserving it as in the Ammonoidea and Dibranchiata? Would Rather 
have Nanno with its immense protoconch not a nautiloid, and its close 
allies, Kndocerdx. CtDiwrocernx VdyhMrcvux^ l'ilonr<iK, all not nautiloids? 
Or would he, by leaving it outside the ))ale of both of liis divisions, 
regard it as a near expression of Ihe ancestral form of both? The latter 
seems, as already observed, Tiearer the correct inter|)retation of tlie 
structure: but it does ajjpi'ar to coincide with IJather's view which is 
stated thus: •• We are tlierefore not entitled to say that the Ammonoidea 
were cU'rived from the Nautiloidea, although we may not doubt that 
all three orders sprung from a common ancestral stock first evolved in 
far pre-Cambrian times. ■■ .i. m. cl.vukk. 
KitosroN i)i:i<rN(i ruio Dki'osition of tiik IUiji.inoton Li.\ifc;sTOXKs. In 
the October number of the (iKor.ooisT (18!)4), I put forward some evi- 
dence to show that there had been a cessation of deposit during the 
buiUling up of t he Ihirlington limestones, and that erosion took place, 
followed by a renewal of deposition. 1 will now describe strata lying in 
an incliniHl position with all surrt)undings going to show that they were 
thus deposited and that the incliiuition is the result of previous erosion. 
The locality is about three miles north of the city of Turlington in the 
blutfs along the \alles of Flint river. This is rather a small stream 
which traverses the country diagonally from the northwest to the south- 
east. The blutfs are (piite promini'nt and in some places very abrupt, 
although dee[)Iy coveri'd with loess and drift. The north l)lutf is fre- 
([uently broken by deep ravines in which, at a nuinbei-(>f places, rock 
