WHITE.] ‘ GARBONIFEROUS FOSSILS. 167 
midheight of the shell, where the front is sharply rounded to the some- 
what broadly rounded ‘basal margin; posterior margin broadly convex 
or sometimes almost straight and perpendicular, and joining both the 
basal and dorsal margins by abrupt curves; dorsal margin compara- 
tively. short, nearly straight; beaks small; umbones not elevated nor 
very prominent. An indistinctly defined umbonal ridge extends from 
each of the umbones to the postero-basal margin, behind which ridge 
the shell is slightly compressed. Surface marked by concentric furrows, 
which are separated by sharp linear ridges. 
Length of an average-sized example, 7 millimeters; height from base 
to beaks, 44 millimeters. 
This species differs from A. vera Hall, from the same formation, in its 
smaller size, in the slight prominence and want of elevation of the um- 
bones, the greater proportional projection of the front beyond the beaks, 
and in being wider behind than in front, the reverse being the case 
with A. vera. 
Position and locality —Coal-measure strata, Danville, Il]., where it was 
obtained by Mr. William Gurley. 
Genus ALLORISMA King. 
ALLORISMA MARIONENSIS White. 
Plate 41, figs. 3a and b. 
Allorisma marionensis White, 1876, Proc. Acad. Nat. Sci. Philad., p. 31. 
Shell small, elongate, ventricose anteriorly, and laterally flattened 
behind, where it is usually a little broader from base to dorsal margin 
than the anterior portion is; umbones prominent, elevated ; beaks in- 
curved, placed far forward; dorsal margin straight or slightly concave; 
postero-dorsal margin sloping backward to the posterior extremity, the 
greatest prominence of which is at, or a little below, midheight of the 
adult shell; base broadly rounded or s'raight« ned about midway, where 
the slight umbonal flattening of each valve meets it. Surface marked 
by the ordinary concentric lines and undulations of growth. 
Length, 28 millimeters; height, 13 millimeters. A few examples have 
been obtained which are about one-third lar ger than that of which the 
dimensions are here given, but it is an unusually small species. 
Position and locality—Saint Louis division of the Subcarboniferous 
Series, Marion and Mahaska Counties, lowa, where it sometimes occurs 
quite plentifully in both the calcareous and magnesian layers of that 
formation. 
GASTEROPODA. 
Genus EUOMPHALUS Sowerby. 
HUOMPHALUS SPRINGVALENSIS White. 
Plate 41, figs. 1a and 6b. 
Enomphatus-springvalensis White, 1876, Proc. Acad. Nat. Sci. Philad., p. 32. 
Shell rather large; spire much extended for a species of this genus; 
volutions six or seven, gradually increasing in size froin the apex to the 
aperture; moderately flattened upon the distal or upper side, regularly 
