Fic. 1. 
Fig. 2. 
Fig. 3. 
Fig. 4. 
Fic. 5. 
Fig. 6. 
Fic. 7. 
Fie. 8. 
Fie. 9. 
Fig. 10. 
PLATE 19. 
UNIO MEEKII. 22.222 co. eee ---- oe noe ce cee ee enn een ee een e ee teeeee : 
a. Natural cast of the interior of the left valve; natural size. 
UNIO SHOSHONENSIS..---------- ---- e----2 ---- ---- - === +--+ noe === 
a. Left valve; natural size; from Southern Wyoming. 
b. Left valve of another, more elongate example; from White River 
Valley, Northwestern Colorado. 
UNTO, WASHAKIENGIS. 12005-0000 RRS elena 
a. Left valve ; natural size; from near Fort Bridger, Southern Wyo- 
ming. 
b. Left valve of another example; anatural cast in sandstone; from 
White River Valley, Northwestern Colorado. 
SITGGUNTAUPAPILLISPIRA 5.21 1g We sents sigan ue ever ny CO Gene 
a. Lateral view; enlarged two diameters, of a gutta-percha cast of a 
natural mold in fine- grained sandstone. The specimen has 
been a little distorted by accidental pressure in its preservation. 
PLANORBIS CIRRATUS...---..----- -- SiS eeee a eave ee ea ta ol antays everett 
a. View of the upper side; enlarged to two diameters. 
b. View of the under side of the same. 
c. Peripheral view of the same, showing the outline of the aperture. 
IBYAUSIONI NITION CIINKEVNUN Sons ogoqde coacua donded bono ad bo Sa sodscoceasas 
a. Apertural view; enlarged to four diameters. 
b. Opposite view of another example similarly enlarged. 
IPOD TOSOOIONUNN Goo6 cn oce5 oso0 sac oSos0505 0050d6 Se Sbeee0 So OSeueN cose 
a. Apertural view; enlarged to four diameters ; showing the aperture 
filled with a portion of the stony matrix. 
b. Opposite view of the same. 
c. Another view of the same, showing the thickened edge of the 
outer lip. 
IPUPAY ARENUDIAG 2 2c aacia ost iee oernete a eee ere e lees jase eee seer 
a. Apertural view; enlarged to four and a half diameters; the per- 
istome broken away. 
b. Opposite view of the same. 
JOGA, ASBAQVOINGU o655 Sooncn co Gud6 coo Se HoS6 acKO ON d6S0 so09 060060 onde 
a. Lateral view; enlarged to six diameters. 
PHYSA BRIDGERENSIG 2a soe ae Sc ya eS aie causing eee eed 
a. Apertural view ; natural size; a part of the outer lip broken away. 
b. Opposite view of another, more robust example. 
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