Bekdk.] Carboniferous Invertetoates. 47 



ward for quite a distance and end in little disc-like suckers. 

 This tube system is rilled with water, and is known as the 

 " water- vascular system.' ' By filling these tubes with water, 

 and dilating them, the animal is enabled to move along. How- 

 ever long the spines may be, the tube-feet may be extended 

 beyond them. The figures illustrate the hard parts which are 

 generally found fossil. There are at least four kinds known in 

 the Kansas rocks. 



ARCHjEOCIDARIS. 



McCoy, Carb. Foss. Ireland, p. 173, (1844). 



Archaeocidaris trudifer. Plate VIII, fig. 10. 



Archceocidans trudifer White, Prelim. Rep. Invert. Foss., p. 17, (1874): 

 Powell's Rep. Geol. Uinta Mts., p. 89, ( 187(5): U. S. Geog. Surv. West 

 100 Mer., iv, p. 104, pi. vi, f. 8, (1877): Keves, Proc. Iowa Acad. Sci., n, 

 p. 191, (1895). 



White's description : " Interambulacral plates compara- 

 tively broad, rather thin, having an elevated border all around, 

 which is apparently composed of a series of small tubercles ; 

 areolar surface apparently plain ; central tubercle small, per- 

 forated at the center, surrounded at its base by a very slightly 

 raised ring, and immediately outside of that by another ring, 

 which i> so much elevated as to form a little cup with its rim 

 somewhat expanded. Diameter of the largest plate in the col- 

 lection about 20 mm. Spines very long and slender, one of 

 these in the collection having been, when perfect, about 

 12 cm. in length, terete; diameter of the basal ring, which 

 expands from the shaft, greater than that of any portion of the 

 shaft ; diameter of the shaft nearly uniform for more than half 

 its length above the basal ring, the upper portion gradually 

 tapering to a point, (rreatest diameter of the shaft of the long 

 spine referred to, scarcely 5 mm. ; diameter of the basal ring, 

 7 mm. Surface of the spine for a short distance above the basal 

 ring apparently smooth, but, from that portion to the distal 

 end, it is ornamented with numerous small points or incipient 

 spinules, which are often removed by weathering, but in well- 

 preserved specimens they are seen to be arranged around tin- 

 -pine in imperfectly spiral lines. The very long, slender, terete 

 spine, having a basal ring often much greater in diameter than 



