328 Lower Silurian Fauna of Minnesota. 



CAMARELLA BERNENSIS n. Sp. 



Plate IV, figures 4, 5, and 6. 

 Compare C. hemipUcata Hall. 



Length 17 mm., breadth slightly greater, depth 10 mm. 



Shell nearly equivalve, beak of the ventral valve more acute, short and 

 curved closely over that of the dorsal valve. Area very small. Ventral 

 valve with about seven broad plications near the mesial line and a short, 

 distinct sinus embracing three of them; one less plication on the dorsal 

 valve. Immature specimens would have neither sinus nor plications. The 

 specimens are white, in strong contrast to other articulates in the same bed. 



If the specimen figured represents a distinct species it will be charac- 

 terized by nearly equal beaks and equal curvature of the valves. In these 

 two respects as well as in possessing more acute plications and smaller size 

 it chiefly differs from C. hemipUcata Hall. 



From the Camarella bed, at Berne, Dodge county, Minn. 



CAMARELLA OWATONNENSIS 11. Sp. 



Plate IV, figures i, 2 and 3. 



Compare C bisculata Emmons. 



Shell oval, globose ; length 10 mm., breadth 8 mm., depth 7 mm. ; sur- 

 face smooth ; beak acute, coiled tightly back upon the dorsal valve, closing 

 ( ?) the perforation of the beak. On the dorsal valve posteriorly, is a narrow 

 groove or sinus, which bifurcates on the umbo, giving room for a plication 

 which in turn bifurcates nearer the mesial line making three rounded 

 grooves on the dorsal surface. Ventral valve with seven plications, the 

 three central ones arising in front of the umbo, while those ending on the 

 lateral margin arise on the beak. 



From the Camarella bed at Owatonna, Minn. 



CRANIA HALLI n. Sp. 



Plate IV, figures 8, 9 and 10. 



Shell convex, irregular in outline, an indistinct octahedron when the 

 valves ?ire in place. Diameter 10 to 15 mm.; valves always (?) detached; 

 surface smooth, dark colored, concentrically marked by indefinite wrinkles 

 often incrusted exteriorly by Aspidopora parasitica Ulrich, or other 

 bryozoon ; ventral valve apparently always so. Ventral valve distinguished 

 most easily by the internal muscle scars one pair of which is against the 

 posterior margin. Interior surface finely sculptured, showing the position 

 of various organs. The strong convexity of the ventral valve distinguishes 

 this species from C. setegeira Hall, with which it is associated. 



From the Stictopora bed at Minneapolis and vicinity. 



DISCINA CONCORDENSIS n. Sp. 



Plate IV, figures 13 and 14. 



Compare D. pelopea Billings. 

 Shell circular, diameter 10 to 20 mm., compressed, subconical, con- 

 centrically wrinkled (6 to the mm.) ; of these wrinkles about two-fifths are 

 circumferences, the others end on the lateral or posterior lateral surfaces. 

 Beak of the dorsal valve acute, not ornamental, situated about two-thirds 

 the distance from the anterior margin, and inclined toward the posterior. 



