Figs. land 2. 
1. 
2. 
Figs. 3 and 4. 
Figs. 5 to 7. 
5 and ‘6. 
is 
Figs. 8 and 9. 
8. 
9: 
Figs. 10 to 14. 
10. 
1b 
12. 
13. 
14, 
Figs. 15 and 16. 
Figs. 17 and 18. 
Figs. 19 and 20. 
Figs. 21 and 22. 
Figs. 23 to 26. 
23 and 24, 
25 and 26. 
Fig. PAG 
Figs. 28 and 29. 
Figs. 30 to 39. 
30 and 31. 
32 and 33. 
34 and 385. 
36 to 38. 
39. 
PLATH XXXV. 
AMB ONY CHUA GB EIST RUATAC SEE we cleticrelets s wlovere aletepe tetas bls aictale cialevelsveltnicverere oicremstensieteje's 
Nearly an entire cast of a left valve. 
Anterior view of same, with the right valve supplied according to our idea of 
the species. Middle ‘Galena, near Wykoff, Minnesota. 
AMBONYGHIATPEANISMR DAMA SET clillsyctslateveisteny exots stats tate loiadeters i fat obebetak enete cobelateasiste falaletetete (atiers 
Left side and anterior views of a specimen preserving the two valves partly 
opened. ‘‘ Lower Blue” limestone, Mineral Point, Wisconsin. 
JANTOOMNC SHUI AMINNIS} INES) OR po gnicsoo seo cinoad ooo NGddoN cooddsoow DoeNbadadsopsdaa 
Lateral and anterior views of a well preserved fragment of the cast of a left 
valve, showing very obscure concentric undulations, fine radiating strive and 
the sharply defined subrostral lobe. Galena, Carroll county, Illinois. 
An illy preserved cast of a right valve from the middle Galena at Weisbach’s 
dam, near Spring Valley, Minnesota Survey Museum Reg. No. 8342. 
AMBONY CHIASANEY GD AT TNVATe Ela lire ale ac, siekeselencietereredsrniete ior iogneratedusiheisi eee petereiseeieeretel siete 
The cast of an imperfect left valve. The specimen has suffered from pressure, 
reducing its diagonal diameter so that the anterior side curves too uniformly 
into the base. 
Profile view, the right valve ideal Lower Galena, Goodhue county, Minnesota. 
CHIONY CHVAMITAM ET OSA ELAM ta cn pols stetevara ttvatohecracctete petal en elena laye cieveralee oleteloletete lstcistes ete cele 
A small, but unusually well preserved cast of a left. valve showing the impres- 
sions of the posterior adductor and pedal muscles, pallial line and ligamental 
area. This specimen is precisely like those which Hall named A. attenuata, 
but its less quadrate shape is evidently the result of pressure. Trenton lime- 
stone, Minneapolis, Minnesota. 
A left valve of the usual form from the ‘‘Lower Blue” limestone at Mineral 
Point, Wisconsin. 
Imperfect cast of a left valve preserving the muscular scars and a portion of the 
wide ligamental area. 
Anterior view of same, showing the impressions of the upper part of the margin, 
the form of the beaks and the pallial line running down from it. 
Cardinal view of same, showing scars of two small muscles (? pedal) behind the 
beak. One or both of these scars are present in all the Ambonychiide. Lower 
Trenton limestone, Beloit, Wisconsin. 
CLION MG HLA SNUTID IAG Ms pS ie oisvacate one ne ait io wis <i sTatei ale Meee cE tee tee eroreeccia oe areata reacts 
Lateral and anterior views of a right valve, showing the form of the species and 
the comparatively fine and regular cencentric lines. Trenton limestone, Min- 
neapolis, Minnesota. Survey Museum Reg. No. 5099. 
GCLIONY CHEAT RR CTADEM all Ha eije.c eecceeeae sieve cage relies ice on lake em aiole stoleetinle eto sieve 
Lateral and anterior view of a nearly perfect right valve. Trenton limestone, 
Minneapolis, Minnesota. 
CLIONVCHIUAS RH OMBOLD HAG WIT Chics -eisc 1 aictan eile lee als tla ol aiarelayoieieacte cieia citrate tateusi elo aieisiaeoetete 
Lateral and anterior views of the specimen described. Trenton limestone, Min- 
neapolis, Minnesota. Survey Museum Reg. No. 5526. 
CLTONY CHTAS UND ATA MM ONS. cess lotctes vateietevets sini oval clarse see isietcleral eievakrelaveicieeieeteic cietere 
Lateral and anterior views of an excellent cast of a right valve. Middle Galena, 
near Wykoff, Minnesota. Collected by Dr. Robbins and now in the author’s 
cabinet. 
BYSSONYCHIA INTERMEDIA Meek and Wortinen:..........cecescccssccsccesscccncs 
Anterior and lateral views of one of the original types of this species. Galena 
limestone. 
Cardinal and lateral views of a small but typical example from the middle 
Galena horizon, near Wykoff, Minnesota. 
PROLOBEBGAYSTRIATULAG Me PEN LSPs ne «ise. b-leleleelainerie cio ee eieeaeteen ie miseeyeteats 
The left side of a specimen, showing the form and surface markings. Middle 
Galena, near Pleasant Grove, Minnesota. 
MODIOLODON( (2) (GIBB US;6M se SPi-[h occ sors cicielcreders els o'alsieinicisja, ct cleisie stemteratecavete wieivisicieetelsiaiersrere 
The left side of a specimen of the natural size and magnified four and one-half 
times. Upper third of the Trenton shales, near Cannon Falls, Minnesota. 
ARISTHR ELAS NUTLD UL Ay We COMME DISD ies cictevaicre siofaceralavaiera oman tleye letra atuintaterajam cieiereiaiolerete 
Left and right sides of an entire shell, x 4.5. 
Lateral and cardinal views of the largest specimen seen, x 45. 
Lateral and cardinal views of an internal cast, in which the hight is less and 
the inequality of the valves greater than usual, x 4.5. 
Natural size views of three shells. Middle third of the Trenton shales Chatfield, 
Minnesota. 
Outline view of a small left valve from the same horizon at St. Paul. In this 
shell the anterior end is unusually narrow. 
492 
493 
494 
495 
496 
496 
497 
499 
532 
522 
524 
