Bidentate Dome

(Pilsbry, 1899)

Ventridens coelaxis







Taxonomic Information

Gastrodonta coelaxis

Original Combination:


Original Description:

Shell rather widely umbilicate, the width of umbilicus contained 6 to 6 1/2 times in the greatest diameter of the shell; thin, somewhat fragile, yellow-corneous, sub transparent, the last suture readily visible through the base; much depressed, the periphery subangular, upper surface convex; surface glossy, sculptured with irregular wrinkles in the direction of growth lines above, almost smooth beneath, and in favorable lights showing subobsolete spiral striae. Whorls 6 1/2, slowly widening a little convex, the last moderately convex below. Aperture oblique irregularly lunar, deeply excised by the preceding whorl, not calloused inside, two-toothed a short distance within ; one thin and rather short lamella projecting from the lower part of the outer wall, and another smaller one from the middle of the baso-columellar wall; both sometimes wanting; pristome thin and sharp, the outer margin well rounded, baso-columellar margin straightened. Umbilicus well-like, but widening at the opening and showing the penultimate whorl. Alt 3, diani. 6 to 6 1/2 mm.
Cranberry, North Carolina (Mrs. George Andrews).
This species adds another to the long series of mountain snails discovered by Mrs. Andrews, whose success in finding new and rare species has been remarkable. Future students of the snails of this "Cumberland" mountain region will always gratefully remember two ladies who have done much of the pioneer work- MRS. ANDREWS and Miss LAW.
G. coelaxis is intermediate between G. gularis (Say) and G. lasmodon (Phill). It is more widely umbilicate than the former and has a narrower umbilicus than the latter species. There is no callus within the basal lip, such as shows a yellowish blotch in most specimens of gularis.
This species is perhaps what Mr. Binney identified as Zonites macilenta Shuttl. in First Supplement to Terr. Moil. V, p. 143, but is not the macilenta of Shuttleworth, which is an absolute synonym of G. lasmodon Phill. That so good a conchologist as Shuttleworth should have described a known species is readily explicable in this case; " H. lasmodon'' having been described but a short time before in the proceedings of a society probably not in Shuttleworth’s possession, it had not been figured and was not contained in any general work on the shells of America. However this may be, so good a diagnostician as Shuttleworth could have used the words, “late et perspective umbilicata " of no other species of the region, and the rest of the description,* as well as the comparison with Patula, agrees excellently with lasmodon. This conclusion will remove macilenta from the list of valid species and place it under lasmodon as a synonym.
The gularis group of Gastrodonta is a peculiarly perplexing one. Both gularis and cuspidata were originally described as imperforate ', butboth have perforate forms also. G. gularis was described from Ohio and I will be most grateful to anyone who has Ohio specimens, for a few. Shell out, brethren! Mr. Vanatta, who has recently overhauled the series in the Academy collection, informs me that he finds great difficulty in separating G. collisella from gularis, and it seems likely that that form should be ranked as a variety of gularis rather than a distinct species. He finds, too, that there is a narrowly umbilicated variety (already noticed by Binney) and another with notably excavated base, consequently straight baso-columellar lip, and more or less deficient internal teeth. This was named by Mr. A. D. Brown in his collection (now in coll. A. N. S. P.); but pending a thorough examination of the gularis group, it is scarcely fair to worry a long-suffering generation of conchologists with any names for these local races. The genitalia of the various forms should be examined.

Original Description Citation:

Pilsbry, H. A. (1899). Descriptions of new American land shells. The Nautilus. 12(12): 140-142., available online at page(s): 140-141

Ecological Information



Nature Serve Conservation Status:

G3: Vulnerable