PLATE XXXIII 
Figs. 1 to 4. Oras (HEBERTELLA?) BELLARUGOSA Conrad..... ...0...c.sceccceseceeseeeceoes 
land 2. Views of the exterior and interior of a large ventral valve. Galena shales, 
Minneola, Minn. Minnesota Geological Survey collection. 
sand 4. Exterior and interior views of a dorsal valve of the ordinary size. Galena 
limestone near Fountain, Mino. Collection of C. Schuchert. 
Wigshe5s 10st... ORRHIS (PERCTOR DAIS) PLICATELDA- Elalle os. .chavtssest nent = Corson fears aviseeaiee.s sles 
Ventral, dorsal and profile views respectively of an entire specimen. Galena 
shales, Kenyon, Minn. Collection of C. Schuchert. 
Figs. 8 to 13. ORTHIS (PLECTORTHIS) WHITFIELDI N. H. Winchell ......2.5... 020... .00ceeccee ee 
Sand 9. Ventral and dorsal views of one of the type specimens, a natural cast of the 
interior. f 
10 and 11. A view of the ventral valve and profile outline of same of another type speci- 
men. Hudson River group, Spring Valley, Minn. Minnesota Geological 
Survey collection. 
12. The interior of a small ventral valve. 
13. A large ventral valve, abnormal in its growth. Hudson River group, Spring 
Valley, Minn. Minnesota Geological Survey collection. 
Figs. 14 to 16. Orrurs (DALMANELLA) HAMBURGENSIS? Walcott........-...c0eessscerereceseses 
14 and 16. Ventral, profile and dorsal views respectively of an entire specimen referred 
with doubt to this species; 16a, fig. 16 x 2. Trenton shales near Fountain, 
Minn. Minnesota Geological Survey collection. 
Figs. 17 to 22: Orruis (DALMANELLA) TESTUDINARIA Dalman........--.0-0..20s-c0scsceeeeceee 
17 and 18. Ventral and dorsal views of a specimen of this species from the Trenton 
shales, Minneapolis, Minn.; flig. 18 X 2. 
19 and 20. Dorsal and profile outlines of the same specimen, x 2, Minnesota Geological 
Survey collection. : 
21 and 22. Interior of the ventral and dorsal valves, x2. St. Paul, Minn. Collection of 
C. Schuchert. 
Figs. 23 and 24. O. (D.) TESTUDINARIA Var. EMACERATA Hall................00ccccceeseesecsaccece 
Two views, a dorsal and profile, of'a specimen referred to this variety. Hud- 
son River group, Spring Valley, Minn. Minnesota Geological Survey collection. 
ISS i20bO 29 -eel ON (Ds) LDESTUDUN AREA Veli) MTEL UVTI Oty reyejeteseleie elelersialaleleiereraleisielelalehctele) slelnis)ulaletstsleis\ctere 
25 to 27. Ventral, dorsal and profile views respectively of an entire specimen. 
28. Profile view of another somewhat thinner specimen. Minnesota Geological Sur- 
vey collection. 
29, The interior of a dorsal valve in which the parts are strongly developed. 
Hudson River group near Spring Valley, Minn. Collection of C. Schuchert. 
Figs. 30 to 36. OrTHIS (DALMANELLA) SUBAQUATA CONTA ......2. ccc ceee cece cer eceec cee reece 
30 to 32. Ventral, dorsal and profile views respectively of the type specimen of Orthis 
minneapolis Winchell. Trenton shales, Minneapolis, Minn. Minnesota Geo- 
logical Survey collection. 
33, 34 and 34a. Dorsal, ventral and profile views of a specimen in which the fold and sinus are 
obsolete and the tubular strie conspicuous. Trenton shales, Minneapolis, 
Minn. Collection of C. Schuchert. 
35. Interior of the ventral valve, x 2. (After Hall.) 
36, Interior of the dorsal valve. (After Hall.) Base of the Upper Buff limestone, 
Minera! Point, Wisconsin. 
Figs. 37 to 39. O. (D.) SUB&QUATA var. CONRADI N. H. Winchell.............0-sseceeecceeseeees 
37. View from the dorsal valve of a typical example of this variety, x 2. 
38 and 39. Ventral and profile views of the same specimen of the natural size. Trenton 
limestone, Minneapolis, Minn. Minnesota Geological Survey collection. 
Higss40) to, 425 O2(D:) susp aAQuaTAnvar: PER VETAs CONTAC. - celle ainleleleeiciotl= alec clecn cis viele seals osc vie 
40 and 41. Ventral and dorsal views of the type specimen of Orthis media Winchell. Base 
of Trenton shales, Minneapolis, Minn. Minnesota Geological Survey collection. 
42. View from the dorsal valve of Conrad’s type specimen of Orthis perveta. (After 
Hall.) Base of Upper Buff beds at Mineral Point, Wisconsin. 
Wigs somtomto. OD) SUB AGUATA Var. GEBBOSA BIINZS)... 65 scciiemiincies «le vaio steicsitleveleinsiees + 
Dorsal, ventral and anterior views of a characteristic specimen of this variety. 
Trenton shales, Minneapolis, Minn, Collection of C Schuchert, 
436 
437 
440 
441 
445 
446 
449 
450 
