a4 
LAMELLIBRANCHIATA. 559 
Vanuxemia subrotunda.] c 
Hist. Sur. Minn., p. 239.) On comparison it proved to have a thinner shell, to be more 
erect and more rounded in outline, also more ventricose and with a stronger umbonal 
ridge, while there are only two cardinal teeth instead of three or more. A fourth 
form I propose soon to describe, in one of the periodicals, under the name of 
V. gibbosa. -It is from the lower Trenton of central Kentucky, and differs from 
the present species in being more gibbous, in having larger umbones, almost 
terminal beaks:and more obtuse anterior side. A fifth is associated with the 
preceding in Kentucky, and also occurs in Tennessee. It is a very thick shell and 
attains to larger size than V. hayniana, from which it differs further in its form 
which is higher and straighter and more obtuse in front. But the principal differ- 
ence lies in the ligamental area which is at least twice as high as in adult examples 
of Safford’s species. The area is shown in four specimens and in all of them its hight 
is 4 mm. or more at the middle and in one it is quite 5mm. For this form | propose 
the name Vanuxemia cardinata. Finally a sixth form of this type is known to me 
from about twenty very perfect specimens that I owe to the liberality of Prof. J. M. 
Safford. He collected them at “Haynies,” the locality in Smith county, Tennessee 
from which he obtained also the types of his “Cyrtodonta hayniana.” Yor the present 
I shall arrange these specimens as a small variety of V. gibbosa, since they agree 
much better with that species than with true V. hayniana. : 
Formation and locality.—The types of this species are from the Trenton limestone (middle Nashville 
beds of Safford) in Smith county, Tennessee. In Kentucky the species occupies two narrow horizons 
separated by more than 100 feet of strata. The first is at the base of the Trenton limestone in Mercer 
county at a point about three miles south of High Bridge, where the decomposed limestone has left 
numerous silicified shells and cystidrans. The second horizon, which is near the top of the Trenton, 
is exposed at several points along the Cincinnati Southern railroad between Burgin and Danville. In 
Minnesota the species seems to be restricted to the Galena shales, in which it occurs as casts of the 
interior at several localities in Goodhue county and at St. Paul. Good specimens are rare. 
VANUXEMIA SUBROTUNDA ey Sp. 
PLATE XXXVIILI, FIGS. 36—38. 
This species differ from V. hayniana Safford sp., to which it is doubtless very 
closely allied, in its more uniformly rounded outline, broader anterior end and 
shorter hinge line, and in having the beaks smaller and situated farther behind the 
anterior extremity. The convexity of the valves also is less, and the shell is thin- 
ner, particularly in the umbonal and anterior parts where the internal thickening 
is so little that no perceptible sulcus nor ridge is left in casts of the interior. For 
the same reason the beaks on casts must be more rounded and larger, so that how- 
ever much the exterior of the two shells may resemble each other, casts of the 
interior would be distinguished very readily. V. nana Ulrich, from the upper Trenton 
in Kentucky, is asmaller shell; with more ventricose valves, better defined umbonal 
