Fig. 
Figs 
Figs. 
Figs. 
Figs. 
Figs. 
Fig. 
Fig. 
Fig. 
26 to 
29 to 
s, 32 and 
34 and 
36 and 
38 and 
aie 
32. 
35. 
37. 
39. 
38. 
39. 
ORBICULOIDEA LAMELLOSA Hall (Byiscictere Sintereislereio Zs latavaietaialate vispoleiane o Aetogumnsmenciere siete 
A dorsal valve, provisionally referred to this species. Hudson River group, 
Spring Valley, Minn. Collection of C. Schuchert, 
SCHIZO LER TAME EL OPRASIBTNingSus..c: eee cee eee ere REE ETE GEE EER EEE CEE EEE Ere EEE 
A dorsal valve. 
A ventral valve, showing the small oval pedicle opening. Middle Galena lime- 
stone, Mantorville, Minn. Minnesota Geological Survey collection. 
Natural cast of the interior of the ventral valve. pa, posterior adductor scars. 
Hudson River group at Spring Valley, Minn. University of Minnesota col- 
lection. 
SCHIZOCRANTA IIT OS AU CEallll sreneh seas bre tee Renee eee eRe EERE EERE er eeaee 
A dorsal valve, showing the large posterior adductor scars. 
Profile outline of same, attached to a gastropod. Trenton limestone, Cannon 
Falls, Minn. Collection of W. H. Scofield. 
A specimen in which the upper, or dorsal, valve has been remoyed, exposing the 
internal characters of the ventral valve. B, dorsal valve; P, ventral valve; g, 
pedicle groove; 1, walls of groove; x 2. (After Hall.) Hudson River group, 
Covington, Ky. ; 
CRAINTAYSETIG At Hall rey endear ryt eae ee eet ee 
An upper, or dorsal, valve, showing the spiniferous surface of the species. 
Profile view of the same specimen. (After Hall.) Trenton limestone at Mineral 
Point, Wisconsin. 
(CHUGSIAN KeF ARTO OSY IS[S TEL, WOM cA connmaanpheodasasdsoonddessonssonboosooonec 
A dorsal and profile outline view of the type specimen. Trenton limestone at 
Minneapolis, Minn. Minnesota Geological Survey colleetion. 
CRANTAS TRENTON ENSTS #Elallll cea meet or secre hace cecet ce cee ce eee ne eeEe eee CR EE RCCEE 
Dorsal and profile views of the type specimen. (After Hall.) Trenton limestone, 
Middleville, New York. 
CRAN TELAT (2) Uae CELL y FLA eee ieee aie tge ee ta nde en ee me an 
A cast of the interior of the ventral valve, somewhat restored on the right side, 
showing the strong anterior and very obscure BOSTENOX adductor impressions, 
and the marks of the vascular sinuses. 
The internal cast of a dorsal valve referred to this species, Showing the muscular 
scars and the sigmoid vascular impressions. (After Hall.) Trenton shales, 
Minneapolis, Minn. Collection of C. Schuchert. 
PHOLIDOPS TRENTONENSIS, Var. MINOR, 0. Var. ... .--e.ceccececccccesececeveeecs 
A dorsal valve (?), x3. Trenton shales, St. Paul, Minn. Collection of C. 
Schuchert. 
LINGUIEAC MODEST AU IT Chica taee cera eee eee eee eee eee ene Ere 
Ventral valve of a small specimen x 4, and outline of the natural size. 
DIN GULAZC VADER AT AS NYS Daa qaame eect ence aa even ae eeT earn emer eee 
Ventral valve of an average sized specimen x 3, and outline of natural size. 
365 
370 
372 
373 
374 
375 
