552 THE PALEONTOLOGY OF MINNESOTA. 
[Vanuxemia rotundata. 
Formation and locality..-Upper part of the Trenton limestone, Minneapolis, Minnesota. The 
illustrated specimen was found by Mr. A. D. Meeds and kindly given by him to the author. The other, 
a much smaller and doubtful cast, belongs to the survey collection and bears the museum register 
number 8329, 
VANUXEMIA ROTUNDATA Hall. 
PLATE XXXVIII, FIGS. 8—14. 
Cypricardites rotundata HALL, 1861. Rept. Supt. Geol. Sur., Wis. p. 29; 1862, Geol. Rept. Wis., 
vol. i, p. 38, fig. 7, and.p. 437. 
Cypricardites rotundatus (part.) WHITFIELD, 1874. Geol. Rept. Wis., vol. iv, p. 208. (Not the speci- 
men illustrated—pl. V, fig. 1l—which belongs to V. suberecta ULRICH.) 
This species is very similar to V. dixonensis Meek and Worthen, and in another 
direction quite as much like V. suberecta Ulrich. Still, as it is very constant in its 
peculiarities, and not at all difficult to distinguish, it should be recognized as a dis- 
tinct species. From the first it differs in being shorter from the beaks to the base 
and therefore circular rather than ovate in outline. The form of the casts, the only 
condition in which the species has been observed, is more erect, the beaks curving 
much less forward so that the anterior margin projects considerably beyond them, 
The anterior sulcus is on the whole stronger, the pallial line more distinct, and the 
average size of the shells little more than half what it isin V. dizonensis. In other 
respects, including the hinge, the two species are practically indentical. Hall says — 
there are two posterior lateral teeth in each valve, and Whitfield one or two, but in 
all the specimens seen by me (about fifty), their number was not less than two and 
oftener three. 
Compared with V. suberecta, a form that was united by Whitfield with V. rotun- 
data, the latter is found to be more oblique, with the anterior end longer and more 
rounded above, the sulcus stronger, more curved, narrower, and without the small: 
ridge which is included in the sulcus in that species. Nor is the anterior boundary 
of the sulcus, especially beneath the muscular scar, so much thickened. There are 
furthermore some differences in the backs of the two species, the hinge line being 
less sunken, the dorsal ridges more obtuse, and the outline, in a side view, straighter 
and even a little concave behind the beaks in some casts of V. suberecta. The hinge 
of the latter is not fully known, but so far as our knowledge goes, it adds another 
difference in the greater obliquity of the cardinal teeth. The survey collection con- 
tains two examples (Mus. Reg. No. 8321) of an unusually convex small variety of this 
species, Four views are given of one of these on plate xxxvIII. 
Formation and locality—Very common in the ‘Lower Blue Beds” of the Trenton formation at 
Janesville and Beloit, Wisconsin. A few specimens from the upper part of the limestone at Minneapolis, 
are doubtfully referred here. ; 
Mus, Reg. Nos. ?5101, 8319, 8321. 
