996 THE PALEONTOLOGY OF MINNESOTA. 
(Liospira americana. 
then the unusual prominence and the sharpness of the curve of the central portion of the outline of 
the lower lip. The angularity of the margin of the umbilicus is of course much less marked in casts 
of the interior than on the shell itself. Still it is always indicated with sufficient clearness to be unmis- 
takable to the trained observer. For comparisons see following species. 
Formation and locality.— Ranges from the base of the Stones River group to the Richmond group. 
The geographical distribution also is very extended, it having been found in Canada, New York, 
Tennessee, Kentucky, Ohio, Indiana, Illinois, Iowa, Wisconsin, and Minnesota. 
Collections.—Geological and Natural History Survey of Minnesota; HE. O. Ulrich; W. H. Scofield. 
Museum Register, Nos. 6765, 7287, 7380. 
LiospirA AMERICANA Billings. 
(Not Figured.) 
Pleurotomaria americana BILLINes, 1860, Can. Nat. and Geol., vol. 5, p. 164. 
Pleurotomaria (or Raphistoma) lenticularis (part.) of American authors. (Not Sowerby’s species.) 
Diameter 30 to 40 mm., hight one-half the diameter or less; apical angle about 130°. 
This species grew to somewhat larger size than L. vitruvia, with which it is generally confounded 
and excusably so, considering the imperfect condition of the great majority of specimens. We have 
found it much less abundant than that species, while its vertical range also is less extensive, being 
restricted apparently to the Trenton period. When good specimens are compared it may be distinguished 
at once from ZL. vitruvia by the different shape of the under lip and a corresponding difference in the 
course of the lines of growth. In L. vitruvia, namely, (see pl. LXIX, fig. 4) the central portion of the 
lower lip projects greatly forward, the anterior outline being sharply rounded in consequence. In 
L. americana, on the other hand, the projection is much less and the curve of the outline, therefore, 
broader, the conditions being about as in Z. micula and L. progne. (See pl. LX VIII, figs. 24 and 38.) 
When the aperture is imperfect and the lines of growth are not preserved, we must depend upon the 
characters of the umbilicus, which is a little wider and less abrupt in casts of L. americana, while the 
shell itself presents no sign of the angulation which encloses the umbilicus in ZL. vitruvia. Where casts 
of the interior only were available we found it sometimes impossible to distinguish them from L. progne, 
but fortunately it is very rare to find casts of Z. americana in which the umbilical cavity is freed 
entirely of the matrix. This fact affords an almost infallible clue, for, if the cavity contains any of the 
stony matrix in which the fossil was imbeded, the observer may rest assured that the spscimen is not 
one of L. progne. In the latter species the relatively large umbilical space is completely occupied by 
shell-matter, so that the cavity remaining after the dissolution of the shell could not, under ordinary 
circumstances, be filled with matter of the same kind as that which fills the interior of the whorls. 
Formation and locality.—Stones River group, Lebanon, Tennessee; Black River group, Maury county, 
Tennessee; Trenton group (Fusispira bed), Fillmore county, Minnesota; also several localities in 
Manitoba. 
Collections.—Geological and Natural History Survey of Minnesota; E. O. Ulrich. 
Museum Register, Nos. 7348, ?7395. 
Liosprra PROGNE Billings. 
PLATE LXVIII, FIGS. 38—44. 
Pleurotomaria progne BILLINGS, 1860, Can. Nat. and Geol., vol. 5, p. 163. 
Width 25 to 35 mm:; hight about half the width; volutions four to four and a half; apical angle 
about 120°. 
This is another of the forms that, especially where it occurs as casts of the interior, is generally 
referred to as Raphistoma lenticulare =Liospira americana Billings sp. Although casts of the interior 
