502 PALEONTOLOGY OF ILLINOIS. 



upper side the base gradually contracts into a flattened or sub- 

 cylindrical stem which soon expands again into a bifoliate, fan- 

 shaped frond, from 1.5 to 4.0 mm. in thickness, and several 

 cm. in width and height. The base, stem, and lower portion of 

 large examples is covered with a faintly striated dermatic crust. 

 Above this the surface presents solid sub-stellate maculae, four 

 or five mm. apart, bordered by apertures very slightly larger 

 than the rest. In the perfect state the apertures are oval, 0.12 

 to 0.15 mm. in length, with the lunarium on one side more or 

 less elevated. In the ordinary state of preservation they ap- 

 pear much larger (about 0.2 mm.) and the interspaces corres- 

 pondingly narrower. The apertures are regularly arranged in 

 intersecting lines, sometimes with six, but more commonly with 

 seven in three mm. Interspaces generally a little elevated, and, 

 when well preserved, covered with fine flexuous striae. These 

 also occur on the surface of the maculae. 



The flabellate zoarium of this species is such a constant char- 

 acter that it suffices to distinguish it from all others. Wei 

 preserved fragments may be recognized by the striate inter- 

 spaces. 



Position and locality: St. Louis group; Spergen Hill, Indi- 

 ana, where the specimens are silicified and impregnated with 

 iron. 



DlCHOTRYPA LYROIDES Ulrich. 

 PI. LXXVII, flg. 2-2/j. 



Zoarium a free lyre-shaped frond, with thick rounded solid 

 margins, diverging from a more or less rounded base at an 

 angle of about 60. The margin is not abruptly thickened, yet 

 is almost twice the thickness of the celluliferous central portion 

 of the frond, which varies in thickness between two and three 

 mm. The height of the example figured must have been at least 

 five or six cm. Surface with broad, rounded, and variously ele- 

 vated monticules, arranged in diagonally intersecting series, be- 

 tween four and five mm. apart, measuring from center to cen- 

 ter. Summits of monticules occupied by solid, circular or sub- 

 stellate maculae, bordered by a row of apertures a little larger 

 than the rest. Apertures circular, slightly oblique, about 0.14 



