432 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



than the radials ; quadrangular. Second costals a little lai'ger ; irregularly 

 pentangular. DLsticlials in two rows, the upper wider and obtusely axillarj'. 

 Palmars two, the plates of the upper row smallest, constituting quite fre- 

 quently a part of the free arms. Arm openings placed at equal distances, 

 except the two facing the anal interradius, which are somewhat farther apart. 

 Arms normally twenty, but varying from eighteen to twenty-two ; rather 

 short, slightly flattened at the tips. Interbrachials from three to five, in two 

 or three rows ; those of the second row varying in height. The anal inter- 

 radius generally has four ranges ; 3, 3, 3, 2, arched over by the palmars. 

 Ventral disk a little shorter than the dorsal cup, hemispherical ; the plates 

 rather large and of neai'ly uniform size. Anal tube subcentral and com- 

 paratively short. 



Horizon and Locality. — Upper Burlington limestone ; Burlington, Iowa, 

 Henderson Co., Ills., Palmyra, Mo., and at all localities where rocks of that 

 formation are exposed, this species being one of its most abundant and 

 characteristic fossils. 



Remarks. — Dizygocrinus rotimdus is the most common species of the 

 Burlington group ; it occurs most abundantly in the white crystalline layers 

 of the middle part. The number of arms is quite variable, we have speci- 

 mens with 18, 19, 20, 21, and 22 arm openings. The arms, which are rarely 

 preserved in this species, are .simple, there being but one arm to each open- 

 ing in all our specimens except one, which has a single paired arm in one of 

 its rays. 



- Hall's " Adinoerinus " ohlatus is a depressed Dizygocrhms rotimdus with 

 twenty-two arms. 



Dizygocrinus dodecadactylus (Meek and Woethen). 

 Phte XXIX. Figs, la, h, c. 



1861. Actimcrinus dodecadadi/lus — JIeek and W. ; Proceed. Acad. Nat, Sci. Phila., p. 131. 



1866. Adinoerinus (Satocriiias) dodecudaciyltis — M. and W. ; Geol. Rep. Illinois, Vol. II., p. 205, Plate 



15, Figs. 3a, i, c. 

 1873. Batocriims dodecadacti/lus — Meek and Wobthen ; ibid., Vol. V., p. 36S. 

 1S81. Batocrims dodecadactylus — W. and Sp. ; Eevision Palaeccr., Part II., p. 166. 



Probably an early phase of Dizygocrinus rotimdus in a persistent form. 

 It is a considerably smaller species, and has twelve instead of twenty arms. 

 Calyx globular, the ventral disk as high as the dorsal cup. Plates smooth, 

 suture lines moderately distinct. 



Base short, rounded, excavated at the bottom. Eadials large, wider than 

 long. Costals small, twice as wide as long, the upper one axillary, support- 



