Figs. 
Figs. 
Fig. 
Fig. 
Figs. 
Figs. 
Figs. 
Figs. 
land 2. 
3 to 
3 and 
2 
5 and 6. 
9 and 10. 
11 and 12. 
13 and 14. 
13. 
14. 
15 and 16. 
15. 
16 and 16a. 
Figs. 17 and 18. 
Figs. 
Figs. 
Figs. 
Figs. 
Figs. 
Figs. 
19 and 20. 
19. 
20. 
21 and 22. 
23 and 24. 
25 and 26. 
27 and 28. 
27. 
28. 
29 and 30. 
PLATE XXXVI. 
MODIOLOPSIS SIMIDIS Ulrich. . 2.2... .c0 cece cee cnvece vane serves ae cceenccdareeress 
(See also plate x11, fig. 19.) 
Dorsal and anterior views of the original type of the species. Middle third of 
the Trenton shales, Minneapolis, Minnesota. 
MODIOLOPSIS ARGUTA, 1. SP... ccc se ce ete e semen eet eee tnen eee e scene ee csseneeeas 
The right side and a dorsal view of a good cast of the interior. Middle third of 
the Trenton shaies, near Fountain, Minnesota. 
A smaller testiferous specimen, imperfect posteriorly, of the natural size and x 2. 
Chatfield, Minnesota. 
MODIOLOPSIS NANA, D. SP. 1.2 ce cece eee ee cree tet teeter nee ee neces estesassecrens 
Right side of a well preserved cast of the interior. Galena shales, Cannon Falls, 
Minnesota. 
MODIOLOPSIS MYTILOIDES Hall...... 2... ccc e cece ce ects ns ett t eres cnnsseesscsens 
Cast of a left valve. Middle Galena, near Wykoff, Minnesota. 
MODIOLOPSIS CHATFIELDENSIS, 0. SD. 22. see e cece ee teen cence eee eee e eee eee erenees 
Right side of a cast of the interior, of the natural size and x 2. Middle third of 
the Trenton shales, Chatfield, Minnesota. 
MODIOLOPSIS OBSOLETA, 1. SP... .-.-- ence cece cece en mee ee cece eect ence tenes Med aSc8 
Testiferous left valve, of the natural size and x 2. Upper part of the middle 
third of the Trenton shales, Goodhue county, Minnesota. 
WOOO) Wb-cONiAeUC (Sy [0G No doaeoourcacsnedonooonndgocodd Oooo soon 50s coed Oud 
Cast of the interior of a right valve. The specimen is a little imperfect in the 
anterior third. Geol. Survey Mus. Reg. No. 8374. 
Well preserved fragment (anterior part) of a cast of the interior of a left valve. 
Survey Museum Reg. No. 8375. Hudson River group, Granger, Minnesota. 
IMODIOMORSISE CONG AbyeAun Wlits1C lateryereretersisfeteyajaietalai= ciate rete olekefalaiats etctersleia tere) s1-telonelou teers) “falar 
The specimen described, a testiferous right valve, of the natural size. 
Lateral and dorsal views of same, x 2. Upper part of the middle third of the 
Trenton shales, Goodhue county, Minnesota. 
A VVAEL I TURV ANY AHIS TAGES UES @/AUEUUN AUT A uaT et SO )atetntevenalielcimiel elelsteleleizisietereleucrsie clei siclejsieiaiausiatelelalars Cin\-l<letals 
The right side and an antero-dorsal view of a cast of the interior, showing the 
form of the shell and obscure traces of radiating strize on the posterior part. 
Middle Galena, Goodhue county, Minnesota. 
WHITEAVESIA MODIOLIFORMIS Meek and Worthen............. csscceeeeee eee cees 
The left side of an internal cast, Beloit, Wisconsin. Survey Mus. Reg. No. 8341. 
View of the original type of the species. In the drawing the base and the ante- 
rior end is restored and the right valve tilted, so as to give an exact dorsal 
profile. ‘‘Lower Blue” beds of the Trenton formation, Mineral Point, Wis- 
consin. Illinois State Museum. 
COLBONRYASDEMISS AG SIeUS Dp eet tere iter re eieteia et derckettel tetererereletoteremteleleieiadetelerotclterietetelstetetctehers 
The nearly perfect shell upon which this species is founded; of the natural size 
and x45. Middle third of the Trenton shales, Chatfield, Minnesota. 
ORTHODESMA SUBNASUTUM Meek and Worthen ............ cee. eeecreretceee cess 
Lateral and dorsal views of an entire cast of this species. Galena limestone, 
. . . \ 
Dixon, Illinois. 
OREHODESMAMSC Hie) CHEAT elles SO evel heyyy t= leteletVeletclateie ols alone lereiclcteleteieimtstsles/cteveleleterslele r= 
Lateral and dorsal views of a cast of the interior, which is imperfect posteriorly, 
but in good condition otherwise. Middle Galena, Fillmore county, Minnesota. 
Survey Museum Reg. No. 8343. 
THUR WANG PAG Pi AUNVAGH EL call ew Gyo atic cievelictatereteretat aliens ole alerorepetciesavejote etehorelernraietatatsi ais elotarscolaisraste siercre 
Interior of the left valve, as obtained in a gutta-percha impression of a cast of 
the interior. 
Hinge and anterior muscular scar of the left valve, magnified nearly two diam- 
eters. Trenton limestone, Minneapolis, Minnesota. 
MUN TECION aEROEOSN LOMB poocodsatocncacdedoccogoopocnd sSonobnbODUBUDE sopdebondant 
Views of the exterior and interior of a large right valve. Upper part of the 
middle third of the Trenton shales, Goodhue county, Minnesota. 
(OVER. 
507 
508 
508 
509 
511 
509 
516 
515 
524 
518 
518 
512 
563 
