390 PALEONTOLOGY OF ILLINOIS. 



very long, slender, rounded, gradually tapering branches, 

 composed each of a single series of round pieces, generally 

 less than twice as wide as long, with a small central canal. 

 These pieces have their articulating surfaces radiately 

 striated, and could not be in any way distinguished from 

 the joints of the column of many crinoids, if found de- 

 tached. 



From Prof. HALL'S species typus* (which also belongs to the section 

 of the genus with the pseudo-brachial appendages composed, near the 

 body, of a double alternating series of pieces, and bifurcating farther 

 out into two rounded branches, composed each of a single range of 

 pieces pierced by a small central canal), the species under considera- 

 tion will be readily distinguished by its much longer and more slender 

 pseudo-brachial appendages, which have their pieces merely rounded 

 and finely granular, instead of being each provided with a row of small 

 tubercles around the middle. From G. tuberculosus, Hall, (sp.), which, 

 if correctly identified among the specimens before us, has its pseudo- 

 brachial appendages constructed, at the base at least, in the same way, 

 it will be distinguished by having its subradial pieces produced into 

 short pointed spines, instead of being merely tuberculiform. The same 

 character, as well as its larger size, and more robust appearance, will 

 also distinguish it from our G. Jiscellus and G. reticulatus. Hall, (sp.) 



The specimen is too much crushed to afford measurements of the 

 body; but the false arms measure 0.60 inch from the body out to the 

 point of bifurcation, and 0.35 inch in breadth. Each of the branches 

 near the point of bifurcation measures only 0.18 inch in thickness, 

 while one of them can be traced to a length of 2 inches, where it is 

 broken off, and measures 0.13 inches in thickness, the whole length of 

 each branch being probably not less than three inches. 



Locality and position Lower division of the Burlington group, Bur- 

 lington, Iowa. Lower Carboniferous. No. 308 of Mr. WACHSMUTH'S 

 collection. 



* As this species is neither the type of the genus Gilbertsocrinus nor of the sub-genus Goniaster- 

 oidocrinus, the name typus can only serve to confuse and mislead the student in regard to the history 

 and synonymy of the genus, and hence ought to be changed. 



