ART. 16. SOME PECULIAR FOSSIL FORMS MANSFIELD 5 



tive as compared Avilh some of the gioantic specimens referred to 

 Daimonelix. However, the orioin and nature of the fossil specimens 

 from the widely separated regions may be different. The " Harrison 

 beds " are considered to be of nonmarine origin, whereas the bed 

 carrying the spiral form in Maryland appears to be of marine origin. 



In Europe, peculiar spiral forms or twisted structures have been 

 known for a long time. In 1865, Dr. Oswald Heer * called attention 

 to some remarkable spirally twisted structures (Schraubensteine) 

 occurring in various parts of the Molasse, or Miocene, of Switzerland. 

 These structures consist of rodlike bodies about as thick as one's 

 finger, on the side of which are seated spirally twisted branches of 

 equal thickness. The author states that these structures were prob- 

 ably the result of filled-in borings made by some species of Mactrina. 

 In favor of this explanation the author w^rites that Prof. Carl Mayer 

 found a Lutraria samxa Basterot in a specimen taken from a sand- 

 stone near the Martinsbruck, in St. Gall. The author also says, on 

 the authority of Doctor Biedermann, that the " screwstones " are 

 found in the uppermost layer of the lower fresh-water Molasse at 

 the boundary of the marine Molasse, which has furnished the material 

 for them. 



In 1901, Ludwig von Amnion ^ described a peculiar spiral form un- 

 der the name Daetrionhelix kravieri from the cyrena-bearing marl in 

 Peissenberg, Germany. The coil of the fragment*' measured 13 cm. 

 in length and over 5 cm. in diameter. The greater diameter of the 

 spiral whorl in cross section measured 20 mm. The specimen was 

 obtained in a mine from a bed overlying the principal coal-bearing 

 series. The illustration ' shows a cast of a muscle shell embedded in 

 a whorl and the intraspiral matrix of a Daemonhelix coil. 



NEW GENUS PROPOSED 



The writer has not formulated any particular theory to explain 

 the origin of the coiled or uncoiled forms from Maryland. There is 

 a suggestion that the central part or core was filled in after the outer 

 wall had been formed. If these forms owe their origin to some or- 

 ganism, as they probably do, that of some marine plant, perhaps a 

 fucoid, seems the more likely. The spiral forms are striking and 

 interesting objects, and for convenience of reference it is desirable 

 to name them. I therefore propose the generic name Xenohelix for 

 the spiral forms and designate Xenohelix Tnaryl and/lea as the geno- 

 type. 



* Die Urwelt der Schweiz, pp. 438, 439, flg. 326. 



5 Ueber das Vorkommen von " Steinschrauben " (Daemonhelix) in der ollgocanen Molasse 

 Obeibayorns, Geognostische Jahreshefte, Dreizehnter Jahrgang, 1900, pp. 55-69, figs. 4, 5, 

 pi. 1, Miinchen. 



» Idem, p. 63, flg. 4. 



' Idem, p. 67, fig. 5. 

 48182—27 2 



