''Quincuncina burkei'' Walker. Plate I, figs. 1 and 4.
Shell of moderate size, subrhomboid, very inequilateral,
subsolid, somewhat inflated; beaks only slightly elevated above the
hinge-line, their sculpture consisting of strong, subcircular
ridges, stronger along the umbonal ridge and curved up sharply
behind, fading out anteriorly and becoming nearly parallel with
the growth-lines; anterior end regularly rounded; base line
curved; posterior end somewhat produced, subtruncate, curving
down rather abruptly and subangulated as it approaches the
posterior point, which is below the median of the disk;
posterior ridge strong and angulated by the junction of the surface
ridges; posterior slope with strong ridges, curving upwards,
extending from the posterior ridge to the posterior margin, these
form a sharp angle on the posterior ridge with heavier ridges
extending downward and forward, which become more or less
broken and tuberculous toward the margin and much weaker
on the anterior end where they assume a rather quincuncial
arrangement; epidermis in mature shells black or sometimes
dark brown, in young shells brown or occasionally
greenish-yellow, in which case obscure radial stripes of darker green are
visible; pseudocardinals double in both valves; in the right
valve the anterior is low and oblique, the posterior strong and
erect; in the left valve the anterior is rather long and projects
obliquely forward, the posterior is larger, erect and more or less
split up; the laterals, two in the left valve and (usually) one in
the right are only a little curved, that in the right valve is
sometimes more or less inclined to be double; beak cavities not
very deep nor compressed; anterior muscle scars well marked,
the superior one deep and extending under the base of the
anterior pseudocardinal; posterior muscle scars distinct, but not
deeply impressed; nacre light purplish, deeper in the beak
cavities and iridescent behind.
Length 51.4, height 31.5, diam. 18.5 mm.
Type locality, Sikes' Creek, a tributary of the Choctahatchee River,
Barbour County, Ala. Also in the Choctahatchee River,
Blue Springs; Pea River at Elamville, Clio and Flemings' Mill
and Campbell's Creek near Clio, Barbour County, and
Hurricane Creek, near Hartford, Geneva County, Ala.
Type, No. 41626, Coll. Walker. Cotypes in the Alabama State Museum and the Carnegie Museum.
This very distinct species was first discovered in the Pea River at Elamville, Ala., by Joseph B. Burke and is named
after him by the request of the late H. H. Smith.
So far as known it is restricted to the Choctahatchee drainage
system.
There is some variation in shape and considerable in
sculpture shown in the series from the several localities listed above.
As shown by the figure the type is quite distinctly biangulated
at the posterior extremity, but in many specimens the upper
angle disappears and the dorsal outline curves directly down to
a sharp posterior point. The surface sculpture is some times
nearly obsolete. This is quite marked in the shells from
Hurricane Creek and the Pea River at Clio. On the other hand the
series from Campbell's Creek are larger and have a much coarser
sculpture than any of the other lots. The largest specimen
seen is in this lot and measures 67.5 × 38 × 23 mm.
The species is extremely subject to erosion and for this reason
the type was selected from the series from Sikes' Creek, which
were in much better condition than those from the
Choctahatchee, which supplied the alcoholic material on which the
generic diagnosis is based.
The description of the beak sculpture is based on a single
young shell from the Pea River, which is nearly in perfect condition.
As stated in the generic diagnosis the affinities of this species
lie clearly with ''U. infucatus'' Con. and ''U. kleinianus'' Lea. It
differs from both in its more elongated shape and less
compressed beak cavities. But the peculiar surface sculpture is the same in all.