220 



PALAEONTOLOGY OF ILLINOIS. 



should have regarded it as synonymous with Rhodocrinus. The following cut 

 however, of the upper part of Goniasteroidocrinus tuberosus of Lyon and 

 Casseday, with its appendages, (in which it evidently agrees with Gilbertsocrinus, 

 excepting in their larger size and position over the interradial spaces), will 

 show, as we believe, sufficiently important differences to separate this type 

 eutirely from the genus Rhodocrinus proper. 



Fig. 10. From these figures, it will 



he seen that this type differs 

 so widely from Rhodocrinus, 

 in the structure and arrange- 

 ment of the appendages of 

 the upper part of its body, 

 that the parts supposed by 

 Phillips and others to be 

 the arms, in Gilbertsocrinus, 

 are really not homologous 

 with the arms of Rhodocri- 

 nus, nor indeed, in any pro- 

 per sense, arms at all, as that 

 term is used in describing- 

 crinoids, but are, on the con- 

 trary, curious additional ap- 

 pendages, composed of two 

 or more ranges of pieces; 

 and although provided with 

 a central cavity through 

 nearly their entire length, 

 connecting with the cavity of 

 the body, they have no open 

 amliulacrul furrow above, 

 nor indeed any traces what- 

 ever of an external opening. 

 Figure A represents the upper side of the vault, with the open- „ , . 



ing (0) and the pseudo-brachial appendages. One of these Consequently they are not 

 appendages and one of the divisions, in part, of another, are , , A' ft 



restored; they are all likewise somewhat more regularly curved Only not arms, out diner 

 than in the specimen. Fig. B represents a side view of the same , • ■, n 11 tl . 



specimen, with the lower part of the body hidden in the matrix, entirely Irom all tne appen- 

 The false arms are here represented as curved in the specimen. -, n ,, , , . 



The asterisk (*) designates the connection of the small, true, pen- ".ages 01 tne DOCiy in any 

 dent arms with the body, as they are seen between two of the ,-. . „-;„,.; 1 „„A 



false arms. C represents the structure of the under side of the Otner known C11U01U, anu 

 false arms, 'between the body and the bifurcation? and D is an en- „„„_. + . i.~„„ „„„»„!,»* t\, a 

 largment of the bases of the true arms as near as can be made out. seem to Dear somewudu me 



same relations to the body that the side branches of the column of Pentacrinus 

 and many palaeozoic crinoids do to the column itself. In addition to this, the 

 parts in this type homologous with the arms in Rhodocrinus and other crinoids, 

 instead of being stout and erect, as in Rhodocrinus, are very slender, long, pendent 



Goiuasi'ZroUloiTiiius tuberoxus. 



