1018 THE PALEONTOLOGY OF MINNESOTA. 
[Hormotoma (?) major. 
Hall under that name. The course adopted having necessitated a new name for the larger form, we pro- 
pose to call it trentonensis, since the species is one of the most characteristic fossils of the Trenton group. 
The respective peculiarities of the two species are perhaps sufficiently brought out by our carefully drawn 
illustrations on plate LXX. The principal differences are that the apical angle is considerably wider and 
the whorls relatively much more depressed in H. bellicincta than in H. trentonensis. These differences, con- 
sidering that they are repeated with an unusual degree of constancy in specimen after specimen, and 
maintained from Vermont and Canada to Minnesota, surely deserve specific recognition. We have not 
seen the aperture of H. bellicincta entire, but in our judgment it is not so much produced below as in H. 
trentonensis. 
Several large species occur in the Trenton that are often extremely difficult to distinguish when, as 
almost invariably happens, nothing but casts of the interior are avaijable; and when these are not good 
the task is in many cases hopeless. However, when some of the outer surface of the shell is preserved the 
difficulties vanish generally at once. Thus we have a form which we have identified with Hall’s Murchi- 
sonia major. The shell of this species is readily distinguished by the character of its suture, the upper 
part of the whorls, instead of sinking in gradually as in H. trentonensis, being flattened and prolonged 
upward at the edge over the preceding whorl so as to form a kind of ‘‘enamelled” suture. In Manitoba 
there is another species (Whiteaves has identified it with M. teretiformis Billings) that, excepting that it 
grew to a much greater size (we have before us a specimen fully 8 inches in length), can scarcely be dis- 
tinguished without the shell and surface markings. These show that the broad band lies lower on the 
whorls (its upper margin lies a trifle beneath the center), while the lines of growth are coarser and, especi- 
ally those coming from below, more decidedly inclined backward in their course to the band. Lophospira 
augustina Billings sp. is another fossil that is likely to be confounded with these species of Hormotoma by 
careless collectors, but the obtuse angulation of the whorls cannot escape the practised eye. 
Formation and locality.—While testiferous specimens of H. trentonensis are everywhere extremely 
rare, casts are common enough in the Trenton limestone of Canada and New York. Specimens of any 
sort are rare in Kentucky and Tennessee. In Minnesota the species occurs rather frequently in the 
Fusispira bed and occasionally in the Maclurea bed. When the strata are shaly the specimens are 
beneath the average in size. 
Collections.—Geological and Natural History Survey of Minnesota; E. O. Ulrich; W. H. Scofield. 
Museum Register, No. 305. 
Hormoroma (?) masor Hall. 
PLATE LXXI, FIGS, 5-7. 
Murchisonia major JLALL, 1851, Geol. Lake Superior Land District, vol. ii, p. 209. 
Not M. major WHITFIELD, 1882, Geol. Wis., vol. iv, p. 244, pl. rx, fig. 4. (=Hormotoma trentonensis 
of this work.) 
Shell large, 80 to 150 mm. in hight, rather slender, composed of about nine whorls; apical angle of 
first four or five turns, which are usually broken or dissolved away, about 37°, of the following four or five 
only 25° to 27°. In a specimen having a maximum width of 65 mm., the last three whorls reach a hight 
of fully 110 mm., while the hight of the aperture, measuring from its lower extremity to the anterior end 
of the suture line, does not exceed 44 mm. In casts of the interior there is a rather large umbilical per- 
foration, the whorls are distinctly separated by an intervening space, the upper edge of the whorls more 
or less sharply angular, and their sides strongly convex in the lower and almost flat in the upper half. In 
the shell itself the umbilicus is very small, the suture shallow and indistinct, the whorls of the spire but 
slightly convex in the lower and middle thirds and gently concave in the upper, the thin upper edge of 
each being turned upward so as to lap over a part of the convex base of the preceding whorl. Aperture 
angular above, only very moderately produced below, on the whole somewhat rhomboidal in outline. 
Notch deep and wide, the deepest part lying about midway between the extremities of the outer lip ora 
little beneath the center. Neither the surface markings nor the band have been observed, but the latter, 
judging from the apertural notch, must lie but a short distance above the suture line. 
