1042 THE PALEONTULOGY OF MINNESOTA. 
{Maclurina cuneata. 
shallowly concave in the center and slightly raised on the outer margins; suture lightly impressed. Right 
(upper) side moderately convex (the greatest thickness or depth varying in different examples from two- 
fifths to one-third the maximum diameter); somewhat conical or subhemispherical, the outer volution 
obliquely flattened and narrowing very rapidly, but in afew specimens somewhat convexly, from the 
periphery to the umbilical margin ; umbilicus deep, conical, and apparently about equal in breadth to one- 
fourth of the maximum diameter, though in all the specimens collected, the test is either imperfect or 
absent at the umbilical margin; aperture obliquely and rather narrowly subtrapeziform ; outer lip appar- 
ently simple; test thick. 
“ Surface of the test on the left or flat side marked with irregularly disposed, but for the most part 
distant, transverse linear grooves or periodic arrests of growth, each of which curve gently backward in a 
very shallowly convex curve, and occasionally with a few striations which run parallel to them. In one 
of the specimens figured which is a little less than four inches in its greatest diameter, and in which the 
whole of the test is preserved on the flat side, there are six of these periodic arrests of growth on the 
outer volution, while the inner whorls are perfectly smooth. In larger but similarly preserved specimens, 
these arrests of growth which are not sufficiently deep to produce any impression on the casts, are some- 
what more numerous and disposed at still more unequal intervals. On the right or convex side the test 
is ornamented with rounded spiral ribs of nearly equal size, and these are crossed by similarly shaped, 
straight and transverse cost, in such a way as to present a somewhat nodulous appearance. The spiral 
ribs, however, seem to be rather broader than the narrow furrows between them while the transverse 
cost are apparently equal in breadth to the regularly concave grooves which alternate with them.” 
The Minnesota specimens referred to this species are all, save one, mere casts of the interior, but 
they agree so well with Whiteaves’ figures and descriptions that there is little room for doubt concerning 
their identity with the Manitoba types of the species. The excepted specimen preserves the shell on the 
inner whorls only, and shows that the first three or four turns are very small and rounded on the lower side. 
The specimen has a width of about four inches, and consists of nearly six whorls, at which rate the largest 
example should make about seven complete volutions. None of the examples seen retain any of the test 
of the convex side of the shell, nor have we seen good moulds of the exterior, hence we cannot say that 
they had revolving lines like those found on one of the specimens described by Whiteaves. 
Formation and locality—Maclurea bed of the Trenton group. Whiteaves (loc. cit.) mentions numer- 
ous localities in Manitoba. In Minnesota the species is not as abundant as the associated M. cuneata, but 
may be found at most localities in Goodhue, Dodge, Olmsted and Fillmore counties, where its particular 
horizon is exposed. 
Collections.— Geological and Natural History Survey of Minnesota; E. O. Ulrich; W. H. Scofield. 
Museum Register, No. 4105. 
Macturina cunEAtTa Whitfield. 
PLATE LXXVI, FIGS. 1-3; PLATE LXXXII, FIG, 46. 
Muclurea cuneate WHITFIELD, 1878, Ann. Rep. Geol. Sur. Wis., p. 75; and 1882, Geol. Wis., vol. iv, p. 
246, pl. 1x, figs. 5—6. 
The diameter in this species, as far as known, does not exceed three inches, while the umbilical 
perforation is very small; otherwise casts of the interior agree almost exactly with those of M. manitobensis. 
A single testiferous example belonging to Mr. Ulrich’s collection has been observed. It is a very small 
specimen, being only 16 mm. in diameter, and embedded in the rock, but on being ground down so as to 
show a vertical section, it brings out as shown in fig. 46, pl. LX XXII, some interesting features. The 
specimen consists of three and ahalf whorls, all gently convex on the lower side but differing considerably 
in other respects. The first two anda half turns are coiled nearly in the same plane, so that they are 
almost entirely exposed on the upper or umbilical side. With the next turn, however, the umbilicus is 
greatly contracted and in the following half turn the normal or rather the specific characters of the shell 
are established, 
