Fig. 1. 
Fic. 2. 
Fic. 3. 
Fig. 4. 
Fie. 5. 
Fic. 6. 
PLATE 28. 
WNIOISHNHNCIUS= rere ceoaeseee bee RS ea be ere eee aioe & 
a. Right valve; natural size. 
b. Anterior portion of a left valve. 
c. Interior view of the same. 
TULOTOMA, THOMPSOND. 2 530 5)54 Gass oo ae oe sicinle een eerete eee uate reicisile 
a. Lateral view of an example from Black Buttes Station, Wyo. ; 
natural size. 
b,c, d,e,f, and g. Examples from Crow Creek, Colorado, showing a 
wide range of variation in surface features. 
h. Basal view of another example, showing the character of the inner 
lip. 
VIVEPARUS PLICAPRESSUS ase Secs oo ae ee Sees TMs os eas 
a. Lateral view; natural size. 
b. Similar view of another example. 
CON BEIMO N.C WA IROCNOC ANDOU ERGs Sooo Sosa geee cosas cee ccc 6225 sce aeee 
a. Side view of an example from Crow Creek, Colorado; natural size. 
b. Another, more robust example, from the same locality. 
VIVIPARUS PRUDENTIUS ..-----------.------- oeidele es Ieee aed ares 
a. Side view ; natural size. 
b. Apertural view of the same. 
MPTANTA: WYOMINGENSISE easiest a ieieiyenen = sane te sersesanele =e eeieereers ie 
a. Side view of a large example, showing the five last volutions; 
natural size. 
b. Another example, showing some of the distal volutions of the spire 
and the beginning of the revolving row of tubercles. 
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