t*LATE XLll. 



Page 



S'igS. t to 5. i/YBODBSMA ACUMINATCM, n. sp 609 



1 and 2. Lateral and cardinal views of a large right valve of the typical form. 



3 and 4. Opposite views, the inner X 2. of a left valve of the var. intermedia. 



5. The hinge of a right valve of the typical form, X 3, showing the retral sweep of the teeth. 



Figs. 6 to 8. LyRODBSMA OANNONENSE, n. sp 910 



6. Somewhat weathered oast of the interior. 



7 and 8. Lateral and cardinal views of a cast preserving the muscular scars. 



Pigs, 9 to U. Allodesma suBELLiPTicnM Ulrich 617 



II ^^^ lo ^*'^^'°^' *"^ lateral views of the cast of the interior upon which the species was founded. 



11 and 12. Lateral and cardinal views of a better preserved cast, X 2. showing the muscular scars, palUal line 



and impressions of the hinge teeth, 

 13 and 14. Restoration of the hinge. 



Figs. 15 and 16. MODIOLOPSISOWENI, n. sp 506 



Lateral and cardinal views of a partial cast of the interior. 

 Figs. 17 and 18. Modiolopsis consimilis, n. sp 50S 



Lateral and cardinal views of an entire silicifled example of this species. 



Fig. 19. MODIOLOPSIS SIMiLis Ulrich 504 



(See also plate xxxvi, figs. 1 and 2.) 

 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. 



Figs. 20 to 25. Clidophorus neolectus Hall 607 



20 to 23. Four views of a rather large specimen from the left side of which the shell has been removed, so as to 

 show the muscular scars and the strong vertical furrow left by the clavicle. The posterior extrem- 

 ity in, this specimen Is narrower than usual. 



24. An oblique cardinal view of a cast of the interior, x 6, showing an impression of the denticulated hinge. 



25. Very perfect cast of the interior of an unusually large right valve, showing, besides thp usual char- 



acters, several obscure rays on the sides and a number of small uraboual scars. Minn. Geol. Sur. 

 Mus. Beg. No. 7338. 



Flgs.26to 28. Otenodonta LOOANi Salter 591 



26 and 27. Oast of the Interior of a right valve. Mlim. Geol. Sur. Mus. Reg. No. 8316. 

 28. Gutta-peroha Impression of same, showing the hinge. 



Fig. 29. Otenodonta 0VIP0RMI8, n. sp 586 



Left side of a cast of the interior, showing the strong muscular scars and other characters of the 

 species. 



Pig. 30. Otenodonta NASTiTA Hall 584 



A small testlf erous left valve of this species from the middle third of the Trenton shales, near Oannon 

 Palls, Minnesota. 



Pigs.31 to 33. Otenodonta 0UNEIFOBMI8, n. sp ; 587 



31 and 32. Two right valves, the first with the posterior constriction more distinct than In the other. 

 33. Hinge of a sight valve, x 2. 



Plgs.34to 3^. Otenodonta BUBNASCTA, n. sp 585 



Three views of a cast of the interior. 



Fig. 37. Ctendonta GIBBERTTLA Salter 587 



(See also text p. 599, fig. 44, f and g) 

 An excellent mold of the Interior of a left valve. 



Figs. 38 to 40. Otenodonta PLANODORSATA Ulrioh 589 



(See also plate xxxvii, figs. 25—28 ) 



38, View of the inner side of a left valve, X 3. 



39, Hinge of same, more highly magnified. 



40, Artificial cast of the interior of a right valve. 



Figs. 41 to 43. Otenodonta CARiNATA, n. sp 589 



41 and 42. A right and left valve, both imperfect and varying sligtly lu outline. 



43. Dorsal view of the left valve. 



Figs. 44 to 49. Otenodonta BITIDA Ulrlch 592 



44. The right side of a small testif erous specimen. 



45 to 47. Lateral, cardinal and posterior views of same, X 2. 



48. The right side of a well preserved cast of the interior of a large example. 



49. Cardinal view of same, X 2, showing scars of the adductor and pedal muscles. 



Figs. 50 to 52. Otenodonta MEDiALis, n. sp 593 



50. Silicified right valve of the species from the middle third of the Trenton shales. 



51. Hinge of same, X 2. 



52. Oast of the interior from the.Galena shales, provisionally referred to this species. 



Pigs. 53 to 58. Otenodonta scofieldi, n. sp 593 



53 to 56. The left side and posterior, anterior and dorsal views of a specimen preserving the shell and showing, 

 among other characters of the species, the sharply angular umbonal ridge. Middle third of the 

 Trenton shales, near Oannon Palls, Minnesota. 



57. Hinge of a right valve, X 2. 



58. The right side of a oast of the interior from the Galena shales, provisionally referred to this species. 



The anterior end is larger than in the typical form. 



[Over. 



