PLATE XL. 



Page. 

 Fig. ]. Cyrtodonta oviroBMis Ulrich 544 



(See also plate xxxix, flg. 46.) 

 j^tnterior view of the type. 



Fgs. 2 to 6. Ctktodonta billingsi, n. sp 538 



2. Cast of a right valve from the lower Tirenton limestone at Cannon Falls, 

 Minnesota. 

 3 to 5. Three views of the best specimen seen. Lower Trenton limestone, Dunleith, 

 Illinois. 

 6. Another specimen from the preceding locality. 



Figs. 7 and 8. Cyetodonta cingulata Ulrich 545 



Anterior view and the right side of the original type. Middle third of the 

 Trenton shales, Minneapolis, Minnesota. 



Figs. 9 to 14. CyktodontA GRANDis Ulrich, and varieties 547 



(See also figure 43, a-fc, p. 547.) 



9. Cast of a large right valve of the var. germana Ulrich. Galena shales, Goodhue 

 county, Minnesota. 



10. Cast of a small specimen from the middle Galena at Lime City, Minnesota. 



This specimen agrees better with the var. germana than with the typical 

 form of the species. .Geol. Sur. Mus. Reg. No. 4102. 



11. A small specimen (cast of a right valve) of the typical form. Middle Galena 



Wylioff, Minnesota. 



12. Interior of the original type of Cypricardites germanus Ulrich. Upper Trenton 



near Danville, Kentucliy. 

 13., Part of the interior of the var. luculentus Sardeson, as shown In a gutta-percha 



impression from a cast of the Interior belonging to the Survey collection. 

 14. A good cast of another right valve of the same variety and from the same • 



locality. Upper beds of the Hudson River group. Granger, Minnesota, Geol. 



Sur. Mus. Reg. No. 8332. 



Figs. 15 to 19. Cktrtodonta TBNBLLA Ulrich 546 



15 and 16. Lateral and anterior views of a large right valve. 



17, Hinge of same. The cardinal teeth are obscure in the specimen and may not be 

 exactly as drawn. 

 18 and 19. Anterior and lateral views of another right valve, differing from the preceding 

 in being more uniformly convex. Upper parfof the middle third of the 

 Trenton shales; Goodhue county, Minnesota. ^ 



Figs. 20 and 21. Vanuxbmia hatniana Safford, sp 557 



(See also plate xxxviii, flg. 32, and text p. 479, flg, 36— iv.) 



Imperfect Interiors of two right valves, showing slight differences in the cardinal 

 teeth. Upper Trenton, near Danville, Kentucky. 



Figs. 22 to 24. Plethogakdia umbonata Ulrich 576 



Three views of the type specimen.. Upper part of the middle third of the 

 Trenton shales, Goodhue county, Minnesota. 



Figs. 25 to 27. Plethocardia suBBKECTA Ulrich 577 



Three views of the type specimen. Galena shales, Goodhue county, Minnesota- 

 Figs. 28 to 30. Whitella quadbangulaejs Whllfleld, sp . . . ._ 566 



28. An Imperfect specimen doubtfully referred to this species. Hudson Elver group. 

 Spring Valley, Minnesota. 

 29 and 30. Lateral and antero-cardinal views of a cast of the Interior from Savannah, 

 Illinois. 



Figs. 31 and 32. Whitella obliquata Ulrich 565 



31. A cast of a left valve from the upper beds of the Cincinnati group, near Blan- 



chester, Ohio. 



32. The Interior of a left valve, showing the hinge with its cardinal teeth, escutcheon 



and posterior internal ligament supports, and faint muscular impressions. 

 The outline is Imperfect posteriorly, causing the shell to appear less oblique 

 than It should be. Hudson Elver group, Spring Valley, Minnesota. 



Figs. 33 and 34. Tbchnophorus subacuttjs Ulrich 614 



Cast of the interior of the natural size and twice magnifled. Trenton limestone, 

 Minneapolis, Minnesota. Geol. Sur. Mus. Eeg. No. 8338. 



Figs. 35 and 36. Tbchnophorus filistkiatus Ulrich . , 615 



Left valve of the natural size and a small portion of the surface enlarged to 

 show the regular character of the fine concentric lines. Upper part of the 

 middle third of the Trenton shales, Goodhue county, Minnesota. 



Figs. 37 and 38. Tbchnophorus divaricatus Ulrich 616 



The type specimen, a perfect left valve, of the natural size and enlarged two and 

 one-half times. Upper third of the Trenton shales, near Cannon Falls, Minnesota. 



