474 THE PALEONTOLOGY OF MINNESOTA. 



(.Ualina nicollcli. 



HALLINA NICOLLETI, n. sp. 



PLATE XXXIV, FIGS. 59-62. 



1892, April 1. Hallina nicolleti W. and S. American Geologist, vol. ix, p. 293. 

 1892, April 9. Zygospira aquila SABDESON. Bulletin of the Minnesota Academy of Natural Sciences, 



vol. iii, p. 335, pi. IV, flgs. 15-18. 



Shell small, rostrate, biconvex, oval or subcircular in outline. Ventral valve 

 convex, point of greatest elevation about mid-length, with a shallow, very narrow 

 sulcus down the center, bordered on each side with a low, rounded ridge, which 

 becomes more prominent toward the anterior margin. The antero-lateral limits of 

 the shell may be smooth or with as many as five low, rounded plications or marginal 

 undulations. Beak strongly incurved, with a small, oval pedicle opening bounded 

 by rudimentary deltidial plates on each side. Dorsal valve evenly convex and 

 trilobed toward the anterior edge; in some specimens the lateral lobes may have 

 as many as six low, rounded plications along the front margin. Calcified brachial 

 supports much as in Hallina saffordi, except that the outer bands are curved later- 

 ally, while the anterior recurved portion is shorter. Articulating processes and 

 muscular scars unknown. 



Hallina nicolleti is easily distingushed from associated species, on account of its 

 small size and camarelloid exterior. It differs from Hallina saffordi in its fold and 

 sinus, and the usually obsolete marginal plications. Its associated species are the- 

 same as occur with H. saffordi. 



Named for Jean N. Nicollet, geologist and geographer of the Northwest. 



Formation and locality. Abundant in the upper third of the Trenton limestone at Minneapolis, 

 St. Charles, Bochester and Fountain, Minnesota; Decorah, Iowa, and in the "Lower Blue beds" at Beloit, 

 Wisconsin. 



Collectors. E. O. Ulrich, W. H. Scofleld and the writers. 

 Mus. Reg. Nos. 339, 434, 436, 438, 440, 652, 660, 8238, 8239. 



