Figs. 1 to 5. 
land 2. 
3 and 4. 
5. 
Figs. 6 to & 
6. 
Tand 8. 
Figs. 9 to 14. 
9 and 10. 
Il and 12, 
13 and 14. 
Figs. 15 and 16. 
Figs. 17 and 18. 
Fig. 19. 
Wigs. 20 to 25. 
20 to 23. 
ge 
Figs. 26 to 28. 
26 and 27. 
28. 
Fig. 29, 
Fig. 30. 
Figs. 31 to 33. 
3L and 32, 
33. 
Figs, 34 to 36. 
Fig. 37. 
Figs. 38 to 40. 
38. 
39. 
40. 
Figs. 41 to 43. 
41 and 42. 
43, 
Figs. 44 to 49. 
45 to 47. 
Figs. 50 to 52. 
Figs. 53 to 58. 
53 to 56. 
PLATE XLIt. 
PAGE. 
LYRODESMA ACUMINATUM, De SPecce ce cece se ccccncsiccsccccconcenccrcnvctcncenereraccrsves soscsresnesseesscucaces 609 
Lateral and cardinal views of a large rei valve of the typical form. 
Opposite views, the inner X 2, of a left valve of the var. intermedia 
The hinge of a right valve of the typical form, x 3, showing the retral sweep of the teeth. 
LYRODESMA CANNONENSE, Nl. SP .....0-eeceeeceeeeeceees Bente Aev'cid Salute cis'e > wisicle os ot Datnaaailans seve sSnee VORAs shea ame 910 
Somewhat weathered cast of the interior. 
Lateral and cardinal views of a cast preserving the muscular scars. 
AULLODESMA SUBELLIPTIOUM UIriCh....... 2.0006 scence eect ee cee e cece ce cee ctncenereneseseecenecsssseee ween shacks 
Cardinal and lateral views of the cast of the interior upon which the species was founded. 
Lateral and cardinal views of a better preserved cast, % 2. showing the muscular sears, pallial line 
and impressions of the hinge teeth, 
Restoration of the hinge. 
MODIOLOPSIS OWENI, n. Sp Soetise ee 
Lateral and cardinal views of a partial east of ‘the inter lor. 
MODIOLOPSIS CONSIMILIS, Nn. SP - Raatideawiashe se winjo cin hes emacleavobaiy aauie<'s™ ko'epe 
Lateral and cardinal views ofa an mentixe Silicified arent ‘of ‘this epaclas! 
MODIOLOPSIS SIMILIS Ulrich ........ ss. .eeee 
(See also plate x XXXV v1, ‘figs. I and 2 2 NE 
View of the right side of the type of this species. The specimen is preserved chiefly as a cast of the 
interior and shows an impression of the shallow anterior muscular scar, 
CLIDOPHORUS NEGLECTUS Hall. berate (Sosananen == eo 
Four views of a rather large eoaotaen oral the left side of. w which the ais has! been ‘removed, so as to 
show the muscular sears and the strong vertical furrow left by the clavicle. The posterior extrera- 
ity in this specimen is narrower than usual. 
An oblique cardinal view of a cast of the interior, x 6, showing an impression of the denticulated hinge. 
Very perfect cast of the interior of an unusually large right valve, showing, besides the usual char- 
acters, several obscure rays on the sides and a number of small umbonal scars. Minn. Geol. Sur. 
Mus. Reg. No. 7336. 
CTENODONTA LOGANI Salter 
Cast of the interior of a right valve. Minn. Geol. Sur. Mus. Reg. No. 8316. 
Gutta-percha impression of same, showing the hinge. 
s and other characters of the 
CTENODONTA OVIFORMIS, 1. SP.cceee cece cece cece cece cnees ceeeaeeeeeeeees 
Left side of a cast of the interior, showing the ‘strong muscular $s 
species. 
OTENODONTA NASUTA Hall .....cccces csccccccecncc ce seccescncccececscrcsscccccensenscsnacssucucsssssassecussesasee 
A small testiferous left valve of this species from the middle third of the Trenton shales, near Cannon 
Falls, Minnesota. 
OTENODONTA CUNEIFORMIS, Nl. SP .s-e- ee ccee cece cece cece ce cece teeeencecccceeeean see sesssbaseeerscscesceesece sees 
Two right valves, the first with the posterior constriction more distinct than in the other. 
Hinge of a right valve, x 2 
CTENODONTA SUBNASUTA, Dl. SP...cccec cee cece er csccenee sees ceccteseeeeeceescncnsanscaccusaceceeces acess arenes 
Three views of a cast of the interior. 
CTENDONTA GIBBERULA Salter.. GC ae Seddce se Utidticrs ¢fanucet [osive's\da\snpaesnaanee 
(See ‘also text p. “599, fiz. ss, t and’ g) 
An excellent mold of the interior of a left valve. 
CTENODONTA PLANODORSATA Ulrich........ 0 ....+- a biaaysesly ta ae cee 
(See also plate XXXvUI, figs. 25—28 ) 
View of the inner side of a left valve, x 3. 
Hinge of same, more highly magnified. 
Artificial cast of the interlor of a right valve. 
CTENODONTA CARINATA, Ni. Sp. 
A right and left valve, both inipertend and varying sligtly in outline, 
Dorsal view of the left valve, 
OTENODONTA NITIDA Ulrich ...... .22. cee ceceecceeees cece seneeereee tenaeecsnsassccsesaneeenssesaces ns ae 
The right side of a small testiferous specimen, 
Lateral, cardinal and posterior views of same, x 2 
The right side of a well preserved cast of the interior of a large example. 
Cardinal view of same, X 2, showing scars of the adductor and pedal muscles, 
OTENODONTA MEDIALIS, .D. SP cc cece cocccesccccceccnccercceecesscteessnesnssee senrscesscessssenee Nias todas 
Silicified right valve of the species from the middle third of the Trenton shales. 
Hinge of same, X 2 
Cast of the interlor from the Galena shales, provisionally referred to this species. 
OTENODONTA SCORTELDY, De SP. .....ces cee ence ccccceccccscssceersenscnss secscces & do. cucwewa sie Vener ene ameter 
The left side and posterior, anterior and dorsal views of a specimen preserv ie she shell and showlng, 
among other characters of the species, the sharply angular umbonal ridge. Middle third of the 
Trenton shales, near Cannon Falls, Minnesota. 
Hinge of a rightWalve, 2. 
The right side of a cast of the interior from the Galena shales, provisionally referred to this species. 
The anterior end ts larger than In the typical form. 
(Over. 
617 
g 
Sul 
584 
580 
592 
