PLATE XXXVI. 



Page. 



Figs, land 2. Modjolopsis similis Ulrich 504 



(See also plate xlii, flg. 19.) 



Dorsal and anterior views of the original type of the species. Middle third of 

 the Trenton shales, Minneapolis, Minnesota. 



Figs. 3 to 6. MODIOLOPSIS AKGUTA, n. sp 506 



Sand 4. Theright side and a dorsal view of a gnnd cast of the interior. Middle third of 



the Trenton shales, near Fountaia, Mionesota. 

 5 and 6. A smaller testiferous specimen, imperfect posteriorly, of the natural size and x 2. 

 Ohatfleld, Minnesota. » 



Fig. 7. MODIOLOPSIS NANA, n. sp 507 



Right side of a well preserved cast of the interior. Galena shales, Cannon Falls, 

 Minnesota. 



Fig.. 8. MODIOLOPSIS MYTILOIDES Hall 508 



Cast of a left valve. Middle Galena, near Wylioff, Minnesota. 



Figs. 9 and 10. Modiolopsis chatfibldbnsis, n. sp 508 



Right side of a cast of the interior, of the natural size and x 2. Middle third of 

 the Trenton shales, Chatfleld, Minnesota. 



Figs. 11 and 12. Modiolopsis omsoleta, n. sp 509 



Testiferous left valve, of the natural size and x 2. Upper part of the middle 

 third of the Trenton shales, Goodhue county, Minnesota. 



Figs. 13 and 14. Modiolopsis excbllbns, n. sp 5J1 



13. Cast of the interior of a right valve. Tbe specimen is a little imperfect in the 



anterior third. Geol. Survey Mus. Reg. No. 8374. 



14. Well preserved fragment (anterior part) of a cast of the Interior of a left valve. 



Survey Museum Reg. No. 8375. Hudson River group, Granger, Minnesota. 



Figs. 15 and 16. Modiolopsis concava Ulrich 509 



15. The specimen described, a testiferous right valve, of the natural size. 



16 and 16a. Lateral and dorsal views of same, x 2. Uppei: part of the middle third of the 

 Trenton shales, Goodhue county, Minnesota. 



Figs. 17 and 18. Whiteavesia subcarinata, n. sp 516 



The right side and an antero-dorsal view of a cast of the interior, showing the 

 form of the shell and obscure traces of radiating striae on the posterior part. 

 Middle Galena, Goodhue county, Minnesota. 



Figs. 19 and 20. Whiteavesia modiolifokmis Meek and Worthen 515 



19. The left side of an internal cast, Beloit, Wisconsin. Survey Mus. Reg. No. 8341. 



20. View of the original type of the species. In the drawing the base and the ante- 



rior end is restored and the right valve tilted, so as to give an exact dorsal 

 profile. "Lower Blue" beds of the Trenton formation, Mineral Point, Wis- 

 consin. Illinois' State Museum. 



Figs. 21 and 22. Colpomya demissa, n. sp 524 



The nearly perfect shell upon which this species is founded; of the natural size 

 and X 4.5. Middle third of the Trenton shales, Chatfleld, Minnesota. 



Figs. 23 and 24. Orthodesma subnasutum Meels and Worthen 518 



Lateral and dorsal views of an entire cast of this species. Galena limestone, 

 Dixon, Illinois. 



Figs. 25 and 26. Obthodesma schucherti, n. sp 518 



Lateral and dorsal views of a cast of the interior, which is imperfect posteriorly, 

 but in good condition otherwise. Middle Galena, Fillmore county, Minnesota. 

 Survey Museum Reg. No. 8343. 



Figs. 27 and 28. Eurymya plana Hall, sp 512 



27. Interior of the left valve, as obtained in a gutta-percha impression of a cast of 



the interior. 



28. Hinge and anterior muscular scar of the left valve, magnified nearly two diam- 



eters. Trenton limestone, Minneapolis, Minnesota. 



Figs, 29 and 30. Matheria rugosa Ulrich 563 



Views of the exterior and interior of a large right valve. Upper part of the 

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



[OVER. 



