FROM THE l'AL/EOZOIC ROCKS OF INDIANA, KENTUCKY AND OHIO. 



Ui 



It is believed that the differences existing between these and any known crinoidal 

 bodies, are at least of sub-generic importance, even if they are not of greater value. It is 

 therefore proposed that these bodies be classified and distinguished under the generic name 

 of Hadrocrinus, and the following generic formula is proposed. 



Basal pieces, . 

 Eadial pieces, 

 Radial pieces, 

 Radial pieces,* 



('Adpdf, full grown.) 



IIADROCEESTUS, n.g. 



Generic Formula. 



. 3. 



. 1st series, 2x5, first large, second cuneiform. 



. 2d series, 2x10, second cuneiform. 



. 3d series, 2x20. " '< 



Other divisions of the rays advance in series of two. 



Interradial fields five, composed of three pieces or more, usually long and narrow. 

 The first resting in the notch between the first radials. 



Interbrachial fields two to four pieces or more; irregular; fields differ in different 

 species. 



Column round, rough, tapering rapidly, and bearing many branches; opening at top of 

 column round; at some distance below the calyx penletotate. Analf field. (?) 



EADIATA. 



ECHINO-DERMATA. 



CEINOIDEA. 



Hadrocrinus plenissimus, n. s. 



PI. XXVI, Pigs. \>, b 1, b 2, b3. 



The specimen figured and described is slightly crushed, and does not exhibit the true 



form. The true form, making due allowance for the crushed condition of the specimen, 



was low and vase-like ; the upper part, above the arms, as shown by other specimens, 



* Some species may bo found which do not extend to the third bifurcation of the ray-bearing piecos. 

 Our specimen of II. plenissimus extends further than the formula. II. discus only bifurcates regularly 

 twice. The formula is intended to receive all crinoids with only two ray-pieces in the primary series. 



f It is not certain that there is any such difference in the sides of the body as that heretofore called 

 the anal side. The difference spoken of in the size and form of the large first radial pieces, may dis- 

 tinguish the anal side. 



