Figs. 
Figs. 
Figs. 
Figs. 
Figs. 
Figs. 
Figs. 
Figs. 
Figs. 
Fig. 
6and 7 
8and 9 
10 and 11 
12 and 13 
14 and 15 
16 to 20 
16 and 20 
17 
18 and 19 
21 to 23 
24 and 25 
26 and 27 
28 
PLATE LX. 
AR CHINACH TZ AG CIN GUT AT AY UilTichiaaeemneteee seo ence eee ae aien te 
Dorsal and profile views of a silicifled shell of this species. Black River group, 
Mercer county, Kentucky, 
LN AGHIOAC GION. IRON IITSE Wie BNOlShaaoonaseos conbubosoeenceon os 6ockea cacannanad sods 
Profile and dorsal views of a cast of the interior showing muscular impressions in 
a very satisfactory manner. A, rostral scars; B, antero-laterals; C, the loop: D, 
a narrow pair flying just within the loop. Stones River group, Beloit, Wis- 
consin. Collection, University of Wisconsin. 
Dorsum of same shell as shown by a gutta percha impression of its matrix. 
ARCHINACELLA RICHMONDENSIS Ulrich... . 22.02... .e cece ccc r eee ececcenesscsstece 
Dorsal and profile views of a gutta percha impression of the exterior of the shell 
which was overgrown by a bryozoan and subsequently dissolved away. Rich- 
mond group, Richmond, Indiana. 
AR CHINAGC HT ADE PRESSA Ui ATICis antennas cease en: aan aoe ae esa 
Dorsal and profile views of the type of this species. Stones River group, Minne- 
apolis, Minnesota. Geological and Natural History Survey of Minnesota, Mu- 
seum Register No. 5523. 
LUA CUONNC TION SGA HAG Wp ANG). cnn oboe sdnoon sbo0 ue oeanaseded suoe se odesboeeE 
Profile and dorsal views of a cast of the exterior from the Phylloporina bed of the 
Black River group at St. Paul, Minnesota. 
ARCHINACELLA SEMICARINATA- U. and S........0.00c.06 cocecevcceccvenee Pease aloe 
Two views of a cast of the interior, showing the carinate umbo and usual form of 
the species. The linear muscular loop is faintly indicated. Clitambonites bed 
of the Trenton group, Cannon Falls, Minnesota. 
ASR CHENACH LIGAG VAD AG SATLCSOUNSD Eee eerie eects tio mater eee eae 
Two views of a rather small specimen of thisspecies. Trenton group (Clitambon- 
ites beds), Cannon Falls, Minnesota. Geological and Natural History Survey 
of Minnesota, Museum Register No. 7417. 
AR CHINA CELTAGDELEDA Sand CSOMS Demy ete -micinis geben e/a-ismie« ccjseisieieis ios scissile 
Two views of an unusually narrow specimen, from Minneapolis. This, like the 
original of figures 18 and 19, grew upon the inner surface of a spiral shell. A 
part of the internal cast of the latter now forms the under side of the specimen 
and gives it the appearance of a bivalved shell. 
A specimen of the usual size and proportions. Goodhue county, Minnesota. 
Two views of a wide cast of theinterior. Near Fountain, Minnesota. Geological 
and Natural History Survey of Minnesota, Museum Register No. 4067. 
All from the Ctenodonta bed of the Black River group. 
ARCHINACELLA INSTABILIS var. INCURVA U. and G..............ecceeveeecrececees 
Three views of an imperfect specimen of this variety, the first of the natural size, 
the others magnified. Ctenodonta bed of the Black River group, Goodhue 
county, Minnesota. 
AR CHENA CH IGIMAGR OL UND ANU AMCs S:eeeciseeieyaceiye clalsiesciiastesiccieme cr etlcie ecco: 
Two views of the cast of the interior upon which this species is founded.» The 
inner border of the continuous muscular loop is sharply preserved, but the 
extreme point of the rostrum and part of the margin on the left side is wanting 
in the specimen. Utica group, Graf, Iowa. 
sents the appearance of this part of the outline in another specimen. The radi- 
ating lines in the right upper fourth of the figure probably represent muscular 
imprints. Between these and the margin the specimen shows numerous very 
fine radiating lines, which we believe correspond with lines upon the external 
surface of the shell. The profile is very nearly as in figure 20 of this plate. Cli- 
tambonites bed of the Trenton group, Goodhue county, Minnesota. 
829 
834 
830 
833 
833 
832 
831 
835 
835 
834 
827 
