Figs. land 2. 
ite 
2. 
Figs. 3 and 4. 
Figs. 5 to 7. 
5and 6. 
1s 
Figs. 8 and 9. 
8. 
9. 
Figs. 10 to 14. 
10. 
ike 
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. 27. 
Figs. 28 and 29. 
Figs. 30 to 39 
30 and 31 
32 and 33 
34 and 35 
36 to 38 
39. 
PLATE XXXV. 
AMBONYCHEA BELDISTRIAT A: EVA 52. crete «nie oy cleyale. wlcletspatererelstskalela) «jn t=ja)aleeatelisTate (olaiel ai statminiaie = 492 
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. 
AMBONYCHIA-PLANISTRUATIA GEV eycjecteroinin ps oie ieeetaccielcteledarsietaletotststa/otolePeicun’e] clalsis [a /ecalslar=/ntole te 491 
Left side and anterior views of a specimen preserving the two valves partly 
opened. ‘‘ Lower Blue” limestone, Mineral Point, Wisconsin. 
AMBONYCHIA AFFINIS, 1. SP... -- 22.00 tec e cece cove cc eencteneecetes teecenetcnenrers 492 
Lateral and anterior views of a well preserved fragment of the cast of a left 
valve, showing very obscure concentric undulations, fine radiating stria 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. 
AMBONYCHIA, AMYGDATINA Mall jerse rc secre teyeiersl= tees eeters ose/alalsllateleteye lula sislagstotsl“\qinietrivtsistes 493 
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. 7 
Profile view, the right valve ideal Lower Galena, Goodhue county, Minnesota. 
CHIONNCHIA TEAMED OSA ELA Se erecrs cielo nvanere -laveyade eta cis oyerey ince lata tcie ms eke rete sjosed=velnferaleiainisiaie 494 
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. 
CLIONY. CHUA: INITTDAG) WeaSDs stele aletetalstel stele tose eiarelaieltes ais eyunetsiey=yoletnts!wixieie)n{oTelnle|yielatelslee referees 495 
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. 
OLTON Y: GEIPAG EG RGOTUAN Ebel]: Seetagnstarete sl atalsieroratstelela nya ercle lalatetarelelals)s\elel=leleia lafelenntalesistatelcia/aisisers 496 
Lateral and anterior view of a nearly perfect right valve. Trenton limestone, 
Minneapolis, Minnesota. 
CUIONY CHITA, RHOMB OLDE Al WD TCH cr ayers ee ete cepeiererehatetete eect re: cies asta ot totataletatel rey apefatale arenatat= 496 
Lateral and anterior views of the specimen described. Trenton limestone, Min- 
neapolis, Minnesota. Survey Museum Reg. No. 5526. 
CLIONYCHIA UNDATA Hmmons ..............+seeeee0s tae macmmonchatauace sot 497 
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 Wortien........ 6 .cceseceeescecnccecceevees 499 
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. 
PROLOBELLA SURIATUTA, Me GEM. Cb S Date «or nyev-tecelclalaistetotoleentewts! emiaroteielosalstu vis veietal=Weln’ateia sl 532 
The left side of a specimen, showing the form and surface markings. Middle 
Galena, near Pleasant Grove, Minnesota. 
MODIOLODON (2) GIBBUS, Ms SP se. cee cscs oo ees eleise cls cvs essce. claivias sielnjeeis'v esa si 00 6 ln 522 
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. 
ARISTERELLA ‘NITIDULA, TD. GD. Ct SP... scene cee nencces wees ccvncncmseseesencess 524 
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. 
