PEAS eieioie: 
Page. 
SPIRIBERA (MATA o5- ore -lanmisissne won tnenceiennre ets oleee anwae eae el sina eee ea ale ee eet eee 141 
Figs. 1, 1a. Lateral and dorsal views of young shell, showing area on each valve. Natural 
size. 
16. A globose form with a lower area on the ventral valve. Natural size. 
lc. A similar form to S. (M.) meristoides Meek. 
ld,le. Ventral and lateral views of a transverse form, with a high area on the ventral 
valve. (S. subumbona-like.) Natural size. See plate xiv, figs. 13, 134. 
Cyrtina DAVIDSONI ...-...-.- -- BIB CBS See eon ocos qaaatenco PEbaSsSnaancoor de Sodecrtase Seeaccoc 146 
Figs. 2,2a,2b. Basal, dorsal, and side views of a strongly-plicated specimen. Enlarged 
to three diameters. 
2c,d,e. Views of area, side, and dorsal valve of a smoother shell. Enlarged to three 
diameters. 
Poppa Og LY AOpen Sri ame ae acon reece so arose Ssoonod hats Sesc cose Gano ccoscusesscacs 143 
Figs. 3,3.a,b. Dorsal, ventral, and side views of the specimen mentioned in the text as of 
the type of S. prematura Hall. Enlarged to two diameters, 
TERS wiz 0s) (HO) Oslo ae BO Bobs He SSee DoS See Sos oes ose Secs os se hao gas Sane Sess sooSse Sone essoss 159 
Fig. 4. Dorsal view of a typical specimen from Independence, Iowa. Natural size. 
7. Same view of a smoother, similar form from Nevada. See plate xv, figs. 5, 5a, b. 
SPIRIBERA) GLABRA, Var. NEVADENSIS =<. oc) asismet= =) stasiae ei eee eta eee scoeas 139 
Fig. 5. Dorsal view of a less transverse specimen than that figured on plate xiv, fig. 14. 
SPIRINERAD UNDIN ERA 6 = ope 9 om'5 onl = == spe wie Vole eam eas = ma iene mt ee olen aloe 143 
Figs. 6,6a. Dorsal and ventral views of a specimen with closely-arranged cencentric stria 
crossing a few low, rounded plications. Natural size. See plate xiv, figs. 11, 
lla, b. 
MGR TSCA (CVV ic) NAS DAS oereje cet lata mteiteere alate tele mi atta Soo Sense Sten Hse SS5SehSre cos 502 148 
Figs. 8,8a,6. Ventral, dorsal, and side views of a well-marked specimen. Natural size. 
PENTAMERUS OTIS 2s- 0/o22 ceiein = Soe wise te relsisinlew oteye tate en eminent aaa ree orate ote eee 161 
Figs. 9,9 a,b,c. Four views of a typical specimen. Enlarged to two diameters. 
