1018 THE PALEONTOLOGY OF MINNESOTA. 



LHormotoma (?) 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 available; 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 Killings) 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. Lophospiru 

 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 

 sorb 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. Scofleld. 

 Museum Register, No. 305. 



HORMOTOMA (?) MAJOR Hall. 



PLATE LXXI, FIGS. 5-7. 



Murchisonia major HALL, 1851, Geol. Lake Superior Land District, vol. ii, p. 209. 

 Not M. major WHITFIELD, 1882, Geol. Wis., vol. iv, p. 244, pi. ix, fig. 4. (Hormotoma trentonensis 

 of this work.) 



Shell large, 80 to 150 mm. in night, rather slender, composed of about nine whorls ; apical angle of 

 flrst 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 "i tin- impeding whorl. Aperture 

 angular above, only very moderately produced below, on the whole somewhat i Iminlinidal in outline. 

 Notch deep and wide, the deepest part lying about midway between the extremities of the outer lip or a 

 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. 



