278 S. WELLER FAUNA OF THE FERN GXEN FORMATION 



ECHINOBERMATA 



CRINOIDEA 



SYNBATHOCRINUS DENTATUS Owen & Shumard 



Plate 11, figure 20 



1852. Synbathocrinus dentatus O. & S., Journal of the Academy of Natural 

 Sciences of Philadelphia (2), volume 2, page 93, plate 11, figures la-b. 



1852. Synbathocrinus dentatus O. & S., Geological Report of Wisconsin, Iowa, 

 and Minnesota, page 597, table 5B, figures la-b. 



1894. Synbathocrinus dentatus Keyes, Missouri Geological Survey, volume 4, 

 page 206, plate 25, figure 14. 



Description. — Dorsal cup obconical, truncate at the base, wider than 

 high, the sides nearly straight from the margin of the basal truncation to 

 the tops of the radials, or diverging a little more rapidly above the tops 

 of the basals. Basal plates a little less than one-half the total height of 

 the dorsal cup; the basal truncation from two-fifths to one-third as wide 

 as the dorsal cup at the top of the radials, somewhat excavated for the 

 attachment of the column. Eadial plates quadrangular, except the right 

 postero-lateral one, wider than high ; their distal faces marked by distinct 

 articular grooves near the outer margin; the inner margin bears two 

 tooth-like processes, divided by a narrow slit-like sinus, which extend 

 upward within the bases of the arms. The left distal angle of the right 

 postero-lateral radial is truncated for the support of the anal plate; sur- 

 face of the plates smooth. 



The dimensions of two dorsal cups are: Diameter at top of radials, 

 10.8 millimeters and 14.5 millimeters; height to base of arms, 7 milli- 

 meters and 8 millimeters ; height to the tops of the distal processes of the 

 radials, 10 millimeters and 12 millimeters. 



Remarks. — Numerous examples of the dorsal cup of this species have 

 been observed in the Fern Glen fauna, but no specimens preserving the 

 arms have been seen. These dorsal cups are not different from similar 

 specimens from the Burlington limestone. The species differs from other 

 members of the genus in its somewhat higher dorsal cup and its nearly 

 straight sides. 



VASOCRIXUS AIACROPLEURUS (Hall) 



Plate 11, figure 21 



1861. Cyathocrinus macropleurus Hall, Description of New Species of Crinoids, 

 page 5. 



1861. Cyathocrinus macropleurus Hall, Journal of the Boston Society of Nat- 

 ural History, volume 7, page 295. 



1879. Vasocrinus macropleurus W. & S., Revision of the Pal?eocrinoidea, part 1, 

 page 96. 



