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Species / Graciliala Cooki


Original description of Anchura ? cooki by Stephenson, 1941:

  • "Shell of moderate size, turreted, apical angle about 28 degrees. Whorls 7 or 8, broadly convex on the sides. On the internal molds the suture is apparently not closely appressed, and on some of them the suture is bordered above by a rather thick, round-crested ridge representing a ridge of callus; this ridge marks the posterior margin of the inner lip, which left the ridge of callus behind it as it grew forward. This ridge was probably overlapped by the shell so that the suture was just back of the ridge instead of in front of it as it appears in the mold. Protoconch not preserved. With the exception of the forward part of the body whorl, and probably several small volutions near the apex, the shell is covered with subangular axial ribs which vary somewhat in form and spacing, but are in general narrower than the interspaces; these ribs number 10 to 14 on each of the larger whorls, and on any one individual tend to increase slightly in number from the body whorl backward toward the apex; the ribs trend downward and slightly forward, and are covered at their anterior ends by the ridge of callus, previously mentioned. On the half of the body whorl farthest back from the outer lip the axials pass down over the periphery and die out on the base; on the half nearest the outer lip they become more widely separated and progressively shorter at the expense of their forward ends. Faint traces of fine spiral threads may be seen on one or two of the specimens and their apparent absence on most specimens may be due to their poor state of preservation. The aperture is elongated and passes posteriorly into an anal notch; anteriorly it passes into a rather short, pointed canal. The outer lip of adults is broad at the beginning of its expansion, but narrows abruptly into a long (10+ mm.), slightly descending projection, or wing, having a minimum width of about 2.5 mm. at the narrowest part preserved; this wing is incomplete on all the available specimens, none of which show the upward projection at the extremity, which presumably would be present on perfect shells; the wing is traversed longitudinally a little above the center by an obtusely subangular ridge which dies out posteriorly at the base of the wing; on the lower margin of the wing about 4 mm. in front of the columella is a broadly rounded projection associated with a broad, shallow, inward plication. The inner lip is broadly excavated, and forms a thick callus which spreads forward several millimeters on the base, and a little upward on the penultimate whorl, forming a ridge which, as previously stated, parallels the suture on all of the larger whorls."

Locus typicus: about 5 miles east by north of Greenville, Hunt County, Texas, USA

Stratum typicum: Corsicana Marl, Navarro Group, Maastrichtian, upper Cretaceous

Dimensions of the cotype shown in plate 56, figure 10: Height about 34 mm., diameter exclusive of the wing about 12 mm.

Anchura ? cooki in Stephenson, 1941; cotypes; plate 56, fig. 7, 8, 9 and 10

  • Image courtesy The University of Texas at Austin


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