PLATE XLVI. 



All the figures on this plat* are magnified about twenty diameters. 



Figs. 1 to 11. TETRADELLA QUADRILIRATA Hall and Whitfleld, sp. 679 



1 to 3. Posterior, side, and dorsal views of a right valve. Middle third of the Trenton 

 shales, Minneapolis, Minn. 



4. Another right valve. Birdseye limestone, High Bridge, Kentucky. 



5. Inner side of a right valve. Minneapolis. 



6 to 8. Three views of a left valve, differing from the usual form in unimportant partic- 

 ulars. Minneapolis. 



9 to 11. Three views of a variety, agreeing with var. simplex in wanting the posterior 

 marginal loculi. Trenton shales, Fountain, Minnesota. 



Figs. 12 to 14. TETKADELLA LUNATIFERA Ulrich 680 



Three views of a left valve of a variety of this species. In other specimens that 

 were found with this one the antero-median ridge is more distinctly double. 

 (See cut, p. 680.) Galena shales, Cannon Falls, Minnesota. 



Figs. 15 and 16. MOOREA ANQULARIS, n. sp 682 



(See also plate M.I n. fig. 89 ) 



Two views of a weather-worn valve, apparently of this species. Trenton shales, 

 Fountain, Minnesota. 



Figs. 17 and 18. MOOREA (?) PEKPLEXA, n. sp 683 



Side and sectional views of the remarkable valve upon which this species is 

 founded. Trenton shales, Fountain, Minnesota. 



Figs. 19 to 22. CERATOPSIS CHAMBERSI Miller, sp 676 



19 and 20. Side and ventral views of a left valve of the usual form. Upper third of the 

 Trenton shales, St. Paul, Minnesota. 



21. Inner side of a more elongate right valve, from the same locality. 



22. Another right valve from the same locality, peculiar in having the small post- 



median ridge divided. 



Figs. 23 to 25. 



Figs. 26 to 29. 



26 and 27. 



28. 



29. 



Figs. 30 to 34. 



Figs. 35 to 38. 

 35. 



36 and 38. 

 37. 



Figs. 39 and 40. 



669 



Fig. 



Fig. 



41. 



42. 



Figs. 43 to 46. 

 4:i to 45. 



46. 



669 



673 



BOLLIA UNOULOIDEA, n. sp 



Three views of a left (?) valve. Galena shales, Cannon Falls, Minnesota. 



BOLLIA SUB.SQUATA, n. sp 



End and side views of a valve of this species. Trenton shales, Fountain, Minn. 



A small valve from the same locality. 



Large and relatively high valve from the same position at Cannon Falls, Minn. 



DILOHELLA TYPA, n. gen. et sp 



Figures of three valves showing slight variations. Upper third of the Trenton 

 shales, St. Paul, Minnesota. 



DRBPANELLA BILATERALIS, n. sp 671 



A right (?) valve of the usual size and appearance. 

 Ventral and posterior views of a left valve. 

 Interior of a right valve. 

 Upper third of the Trenton shales, St. Paul, Minnesota. 



DICRANELLA BicoiiNis, n. gen. et. sp 665 



(See also plate M.I v. fig. 26.) 



Side and posterior views of a nearly complete right valve. Middle third of the 

 Trenton shales, Minneapolis, Minn. 



DlCRANKLLA 8PINOSA, n. sp 665 



(See also plate XLIV, fig. 23.) 



Posterior view of a left valve. 



|M< ILANKI.I.A (?) SIMPLEX, n. Sp 666 



Ventral view of the valve figured on plate XLIV, flgs. 24 and 25. 



1 1 \ 1. 1 .n i.i. \ LAUIOBA, n. sp 656 



Anterior, dorsal, and left side views of an entire carapace. Galena shales near 



Cannon Falls. Minnesota. 

 Somewhat weathered and relatively longer left valve: from the same locality. 



