190 PALEONTOLOGY OF ILLINOIS. 



form, with heavy plates and somewhat indistinct surface mark- 

 ings. Meek and Worthen, in Vol. Ill of this Report, p. 469, 

 PL XVI, Fig. f>, described and figured as P. planus a well pre- 

 served specimen with large, elongate calyx, of the form of P. 

 pratteni, having similar slender arms; and again in Vol. V, 

 PI. Ill, Fig. 5, they figured under the name of P. pJanus, but 

 without description, a good specimen having many diameters 

 in common with the form under consideration. The truth is, 

 there are probably several species of these elongate smooth 

 forms of I'lntycrinus. The plates of those in the Lower Bur- 

 lington are very thin and fragile, so that specimens in good 

 preservation are rare, and the vault is for the most part un- 

 known. More abundant collections will no doubt throw new 

 light upon their affinities, but for the present we are inclined 

 to think the form herein illustrated comes as near to the origi- 

 nal description of Owen and Shumard as any that have since 

 been referred to it. 



Geological position, etc.: Same as the last species. Our own 

 collection. P. planus, as recognized by the Burlington Geolo- 

 gists, is a leading fossil of the Lower Burlington limestone, and 

 has been found at the various localities where that formation 

 is exposed. It has been collected by us in New Mexico, and we 

 have seen specimens from different places in Missouri. 



GENUS DICHOCRINUS. 



DlCHOORINUS INORNATUS (sp. nOV.) W. & Sp. 



PI. XVI, Fig. 1. A specimen with arms, showing the posterior side. 

 PI, XVI, Fig. 2. The same from the anterior side. 



This is the earliest Dichocrinus known to us from America, 

 and perhaps precedes any known from Europe, but nevertheless 

 it has all the characteristics of the genus. Dichocrinus inorna- 

 tus probably has its closest affinities with D. ovatus 0. & 

 Shum., which, however, is beautifully ornamented, the calyx, 

 and especially the radials, are more elongate, and the large anal 

 plate less constricted between the arm bases. It also resembles 

 D. simplex Shum., but the proportions of the plates in the two 



