8 PROCEEDINGS OF THE NATIONAL MUSEUM vol.71 



VON Ammon, Ludwig. Ueber das Vorkommen von " Steinschrauben " (Daemon- 

 helix) in der oligocanen Molasse Oberbayerns, Geognostische 

 Jahreshefte, Dreizehnter Jalirgang, 1900. pp. 55-69, figs. 4, 5, pi. 1, 

 Munchen, 1901. 



WoBTMAN, J. L. On the so-called Devil's Corkscrews of Nebraska : The 

 American Naturalist, vol. 29, p. 403, 1895. 



EXPLANATION OF PLATES. 



Plate 1. 



A, Photograph of Langleys Bluff, St. Marys County, Md. The head of the 



hammer shows the contact between the Pleistocene deposit and the 

 St. Marys formation. See p. 1, section No. 1, for description. 



B, Photograph of a low bluff about one-third mile above the site of the old 



Langley homestead, St. Mary.s County, Md. A — A indicates the 

 probable unconformity between the lower bed and the upper bed. 

 The peculiar spiral and other forms came from the lower bed, 

 occuring more abundantly in the lower part, as indicated by the 

 head of the hammer. See p. 2, section No. 2, for description. 



Plate 2. 



Figs. 1-A, XenoJielix marijlandica Mansfield. Type of new genus and species. 

 Cat. No. 354137, U.S.N.M. p. 6. 



1. Upright position of coil, about three-fourths natural size. 



2. Cross section of peripheral wall cut from specimen No. 1, showing 



porous character of wall. (X 3.) 



3. Photomicrograph of peripheral wall in cross section, cut from specimen 



No. 1. (X 3.) 



4. Cross section of larger end of specimen No. 1, about natural size, show- 



ing peripheral wall and central core. 



Plate 3 



Figs. 1, 2. XenoheUx nwrylandica Mansfield. Topotypes. Cat. No. 354138, 

 U.S.N.M. Slightly reduced. 

 3. Fragment in cross section of XenoheUx marylandica. a, Shows a east 

 of a bivalve shell imbedded in the inner margin of the peripheral 

 wall. Slightly reduced. 



Plate 4 



Figs. 1, 3. Irregular, apparently branching form, taken from the same bed at 

 the same locality as the type of XenoheUx marylandica Mansfield. 

 Cat. No. 354139, U.S.N.M. Slightly reduced. 

 2. Longitudinal section of a nearly straight and tapering form, taken from 

 the same bed and at the same locality as Figures 1 and 3. Hori- 

 zontally placed in the bank. Cat. No. 354140, U.S.N.M. Slightly 

 reduced. 



